I've always been curious about how penis size, or perceived penis size can affect a girl's level of attraction. I tend to think that body language has more to do with it, and that making your pelvis the point of focus is what matters most, regardless of the actual size.
Girls are crazy, illogical creatures, and like their pussies, their minds can get warped, and will warp things out of proportion. If you're game is super tight, a girl will see you as a god, and will chose you over the big-dicked guy with bad game.
Girls do check out guys packages:
And Penis size can make a difference in sex, apparently it matters more to girls than big tits matter to guys:
http://www.penissizedebate.com/
Big dick can probably be roped in with other non-game attributes (like good looks), in that sense, it can be a plus, but you don't need one to get girls, because reproductive qualities only represent a small portion of what attracts a girl.
I know dickless, butchy lesbians who have better game than most guys, and are able to get and keep hotter girls (the fem kind) than most guys as well.
I know people who used to work with Bon Jovi, and it was a big joke amongst the crew (and even Bon Jovi himself) that Jon had a small dick (the joke being that he was this big rockstar).
Also, even if you have a big dick, and if dick size is all that important, there's always going to be someone out there with a bigger one. It's just like that recent thread on celebrities hitting on your girl. There's nothing you can do about it. Don't get attached to any one girl.
There are always going to be bigger fish in the pond, and you have to work with what you've got. Anyway, in the bedroom, you shouldn't be worried about pleasing her, but if you want to see something cool, learn how to make a girl squirt (it's really easy, search the forum).
In my personal experience, I've had lot's of girls tell me that my dick was big, but I still have a lot of confidence/game issues.. and somehow I still have insecurity about my dick! But, I go on. My drive to fuck girls is stronger than most of my fears of rejection.