Ira Glass raised this question recently; or, perhaps, not so much raised it as lamented the way in which people retroactively confer "nerd" status upon themselves. As in, "I was such a big nerd in high school." His basic argument was: no you weren't, or: prove it.
He surmised that most people filter their actual popularity, if not their seeded positions on Homecoming Court, through a sentimental lens of nerddom. "Nerds" experience pain, certainly, but just because one experienced pain in adolescence, does this make one a nerd?
I do seem to hear this self diagnosis a lot from people I know, but then again, maybe that's because these are the friends of someone who does feel she was a nerd (grades 7-9: unequivocally; thereafter: equivocally). Perhaps it's just safer now to admit--or appropriate--one's nerdy past now that we're in the post-Napoleon Dynamite, Colin Meloy, Weezer, Adam Brody, Fancy Nancy, all McSweeney's endeavors, et al. era. Not to mention Judd Apatow and his latest manifesto, Superbad (eclipsing poor old Ben Greenman). I mean, Jon Cryer has Emmy nominations, John Hodgman is a superstar, and Jonathan Ames is dating Fiona Apple. Are people claiming to have been nerds so that we can infer they're destined for greatness, or because it's closure on a difficult and nebulous youth, or what?