I know that Marvel has said he isn't, heck, his tagline was Greatest non Muntant super hero during the Nineties after all! But, wouldn't it be a fun story for Spidey to figure out he actually is a secret mutant? With his mystic background where he was always destined to be Spider-Man, I think you can consider him a mutant. For the Science background story, I think theres a way he could still be a mutant. Nowadays, radioactivity is used in radiotherapy to cure cancer. Maybe when the radioactive spider bit Peter, it didn't transfer powers, the radioactivity caused mutant genes to kickstart all of a sudden, in a way to help build Peter's body, and immune system.

Not saying it's a bad idea but it would involve some major retcons as Reed Richards tested him on an X-gene once or twice already and the X-Men had some issues with him not being a mutant before, etc.

Spider-Man by all means is a meta-human.

He isn't a mutant, and I don't think readers would want him to be....

This has already been talked about already in comics. Professor X in laymen terms said it like this "Spiderman is a MUTATE not a MUTANT! There are many Mutates such as the FF. A mutate is someone who's dna was altered such as the FF and Spider-Man"

No X-Gene, not mutant. Peter is a genius, he would've noticed. So are Stark, Pym and Richards. They've all examined him.

Nope Peter's not a mutant in fact i've noticed recently he's starting to bear similarities to the Black Tarantula. Both of them are Spider-totems, both of them where "chosen" to bear its powers (Peter via whatever the hell chooses Spider-people and Black Tarantula via his bloodline) and both of their abilities seem to improve the older they get (Peter shedding his skin and gaining the "other" powers and Black Tarantula going from a 25 to an 85 tonner due to his age).