I don't think I ever thought about it that much before I joined this site - it was one of those pleasant surprises you got when you got naked with a guy. Kinda like when you meet a guy you really like, you spend the night together and he turns out to be great at oral. Bonus!
Of course, when daydreaming I rather expect every woman imagines her prospective lover(s) to have the qualities that make sex good for her. That doesn't include a big cock for some women and does for others.
I think about it sometimes when I'm talking to or observing men - but because I'm not looking for a man I don't think about it from a personal attraction point of view but just in academic terms.