I've been skinny all my life, and for the most part, it seemed to work against me more than for me in the dating scene. When I'd ask girls why, I generally got one of two responses:
1) 'We like a big cuddly teddy bear, not a skeleton.' I think in a lot of cases what they were really saying is that a bigger guy could likely protect them better, even if only by having an easier time commanding people's respect.
2) 'I wouldn't want a guy skinnier than me.' This one seems to imply either that skininess is inherently feminine, or (more likely) that in a society with a weight problem, a skinny guy makes most women hate their bodies more than they already do. Misery likes company -- if I'm with a big chubby dude, there's a lot less chance I'll get self-conscious about my (real or perceived) image problem. A guy with a gut is more 'real'.
I knew my wife was a keeper when she told me she respected my 11% bodyfat, because it showed her that I was active, energetic, and took care of myself. (I showed her just how much energy my overclocked metabolism can generate, the second night we met

Sadly, women with this attitude, at least in my culture, are scarcer than I originally thought.
To all those guys who've despaired at losing the spare tire, and would envy a guy like me (5'7" / 135 / 30" waist), all I can say is the same thing that many guys with enormous peterpauls tell me: the grass is most definitely not greener.