I like Spidey shooting the webs organically like in the movies and not mechanically.

Peter is somehow a hidden child prodigy with the combined intellects of Sheldon Cooper and Michael Scofield along with a little bit of Gregory House.

" Maybe his parents got him an erector set early on? "

while I agree the shooting webbing out of his wrists 1. is gross and 2. doesn't fit with how a spider would actually do it..but then again do we really want to see him shooting webbing out of his ass? that'd be worse.
 
regardless..him inventing it is just idiotic when you take into consideration the rest of his character. Most importantly his "struggle" for money and helping his aunt etc.
 
If he is smart enough to invent this chemical mixture that acts in this way then he's smart enough to PATENT and SELL IT.  Perhaps making it last longer...and doing so in such a way that doesn't give away that it's the same stuff Spiderman uses..if he can create the shooters to make it mimic a spiders webbing..then he can create a distribution device that makes it look like something else.
 
Not to mention that if Peter can afford to get the compounds that make up this "webbing" mixture..then it's VERY AFFORDABLE to create.
 
He would be a multi-billionaire with just this alone.
 
and..of course..the whole radioactive spider bite was a thing of the times..which is why more current "reboots"/"retellings" go for something more akin to the times we're in NOW....genetic modifications/etc.
 
Either way "natural" webbing not only makes more sense but is less of a stretch for believability..even if coming out of his wrists is odd.
 
It will be absolutely idiotic to see Peter create this chemical compound, a total wonder of modern science (even by todays standards, much less when SM was created) yet struggle with finances and HAVE to take a job as a reporter taking pictures of himself to make money.
 
So yah can't agree with you on this.  If ANYONE invented such a material they would be billionaires...and if Peter is smart enough to create this compound AND the distribution devices (web shooters) then he's smart enough to patent and market it.  As it is, him "inventing" it makes NO SENSE.

 "  In Ultimate Spider-Man [...], the webbing was natural, coming out from his wrists"  

 That's not true at all. It's the 616 Spider-Man who eventually got organic webshooters and the ability to talk to bugs after a lady kissed him, and later he developed fangs and stingers when he ate that one dude's face. 
 
... comic books.

I only like the mechanical ones.
 
But has it been stated that those are mechanical webshooters? Couldn't it just be the opening for organic webs to come out of his wrists?
 
And: Does Spider-Man still have the organic webspinning powers and that stuff coming out of his back ("The Other" storyline) but Mephisto made him forget, or are we supposed to think that never happened?

In Ultimate universe he has also invent webbing and shooters, but with his fathers unfinished formula, so I like that explanation and origin of web shooters. 

I like the organic web shooters. He's always got them on him, he doesn't have to wear bulky wrist things that could get ripped off in a fight, he never runs out of webbing, and if he's in a situation where he can't quickly change into his costume, he can shoot some web on his face, poke out some eyeholes, and commence with the beat down. Thus giving the nickname "web-head" a whole new meaning.

" The whole "webbing out of wrists" thing was icky to me. "

" I only like the mechanical ones.  But has it been stated that those are mechanical webshooters? Couldn't it just be the opening for organic webs to come out of his wrists?  And: Does Spider-Man still have the organic webspinning powers and that stuff coming out of his back ("The Other" storyline) but Mephisto made him forget, or are we supposed to think that never happened? "

invented ones are just plain dumb.  As I said it makes no sense that someone with that level of intelligence wouldn't be selling inventions he made.  Think about it.
 
Web shooter material could be used in so many applications..esp if he modified it to last longer/shorter depending on the application.
 
Think of his new "spider suits" he's inventing in comics...we're talking about a damn kid that is inventing things akin to the Iron Man armor and whatnot...they're genius inventions...why then is Peter struggling with money and having to resort to being a photographer? it makes no sense....
 
"natural" web shooters is the ONLY thing that makes any kind of sense when you look outisde of "derr the character is only as smart as we need him to be...peter can invent these things but not something to patent, sell, and become a billionaire on...DERRRRRRRRRRRRRRRRRRR"

Aaaand thank you G-Man for planting that lovely image in my head. The brain bleach industry would like to express their gratitude.

" invented ones are just plain dumb.  As I said it makes no sense that someone with that level of intelligence wouldn't be selling inventions he made.  Think about it.  Web shooter material could be used in so many applications..esp if he modified it to last longer/shorter depending on the application.  Think of his new "spider suits" he's inventing in comics...we're talking about a damn kid that is inventing things akin to the Iron Man armor and whatnot...they're genius inventions...why then is Peter struggling with money and having to resort to being a photographer? it makes no sense....  "natural" web shooters is the ONLY thing that makes any kind of sense when you look outisde of "derr the character is only as smart as we need him to be...peter can invent these things but not something to patent, sell, and become a billionaire on...DERRRRRRRRRRRRRRRRRRR" "

I mean the fluid itself is the primary focus on how to make it. im sure with a polycarbon fluid, there are several that start out as fluid and can bio degrade when exposed to oxygen. so all you need is an adhesive layer to coat over top of the original base which would act as the tether and the adhesive would allow it to stick much like a spider web.....
  hmm this idea can work just need a degradable solution for the adhesive mix in order to hold a person for a duration of a hour at the most or maybe cut the formulas degradation time to 45 mins to allow police assistance. this bodes research and discussion.

" The main issue I always had was a matter of mass.  He has enough cartridges on his wrist to be equivalent to a can of silly-string.  So with two wrists he has about two cans worth.  This would equate to maybe 40 seconds of shooting.  No say the web susbtance exists to it can be projected and expands in air somehow - this would give him maybe three or four times as much, so every time Spider Man heads out to fight crime, he has maybe 2 and a half minutes or webbing to use.  Thats not a lot.    Even if it is organic, all that matter being expelled from his body has to come from somewhere, and if it is like a real spider would leave him severely dehydrated.  "

Of course he could have patented the web shooters without revealing his identity, he could have just said that he was inspired by Spider-Man when he created them.

Mechanical shooters make me happy 
The organic ones were...... dirty 
 
And who knows, maybe in this new Spiderman world, the compouds were already being developed and he just made a firing mechanism for them or something. Or maybe he is that smart. I never thought twice about it in the comics or the cartoon, I imagine most wouldn't have that big a problem suspending disbelief during the movie either

I haven't read much Spider-Man. I knew that sometimes they were mechanical and sometimes natural, but I had always thought someone else made the mechanical ones for him. My friends had never pointed out to me that Peter actually did that. Granted, I had it in my head wrong, it just seems more believable to me that he wouldn't do it. Reading a lot of the comments here, it doesn't seem right, either. If he's so bright, why does he have a crap job? It seems really retarded to me, now I know the truth. 
 
I do like the natural web shooters. It makes the problem go away, and if you're bitten by a radioactive spider, I don't see why he couldn't have them shoot from his wrists. He mutated, after all. 

you think its ever taken the cops more than an hour to pick up the baddies?

I prefer the mechanical version as it gave them a way of including Peter's affinity for science into the mix.  It also allowed for future inclusion of his scientific skill, when he created alternate web formulas and shooters to tackle new problems.  As reality-bending as comics are, it seems to make things more believable when you see that he didn't miraculously gain every single ability that the spider possessed. 
 
Besides, we all know that it was the Spider-Man from a dark alternate future who made it possible.  Knowing that the world would be doomed without a web-slinging Spider-Man, alternate Peter traveled back in time using a heavily modified Spider-Mobile, and gave him the knowledge of how to built web shooters, while teen Peter slept.  The teen Peter Parker was then able to create a more livable future for all, making it possible for him to ruin his marriage, and reveal his identity to one and all.  Hooray!