Well... I'm not sure I'd always equate "nerd/geek" with "tomboy". The latter I am very fond of, the former not quite so much. Both, however, are indeed preferable in real life to a "glamour girl" sort of gal ... I'd say probably because as a guy I can relate with the former two more than I could an ultra-feminine type. Plus the intelligence, accessibility, and all other reasons mentioned here are all crucial components to a winning personality, IMO.
That said, I prefer the more glamorous look in my private fantasies, as should probably be evidenced by the morph work I do here at the BEA. While I can understand the appeal of the couple of intellectual-type gals mentioned here, it's usually something I look for in the girls I know in real life, rather than distant media figures / characters.
Style counts when you're gazing from afar; substance is what matters when you're up close.
Just some thoughts.