I've been pondering this for awhile, and my only conclusion: Doctor Who. The 10th Doctor, specifically. A smart, attractive, adventurous fellow (dat Tennant) who flies around the universe being funny and saving lives? Sounds like anybody's best friend. Every time I see a description of him online he's described as "Geek-Chic". He wears suits, thick rimmed glasses at times, always a little out-there, and yet seems perfectly friendly and complex, as far as people go. With the huge popularity of Doctor Who, and America's love of emulating Britain (Curse you, Spice Girls!), we had this coming, and we have nobody to blame but ourselves. You either die a Hero, or you resurrect often enough to see yourself become the Villain.
If you take away all the wibbly-wobbly timey-wimey stuff, it's just another boy meets girl show over and over again, with a bit of action and suspense thrown in. Honestly, I think the Doctor Who trend among nerdy girls stems from a sort of "I want to be rescued from my mundane life" mentality that plenty of girls - nerdy or not - idealize. Doctor Who just happens to be that guy for girls who like science fiction right now.
I never thought that my love of British comedy and television ever stemmed from my childhood obsession with the Spice Girls... but all that makes much more sense now.