My cock curves down a rather lot. It is great for blowjobs (only works for 69 if I am above) but for anal it really bothers my partner if he is facing me. It is better if we are doing a reverse cowboy, but usually I bottom (his cock curves beuatifuly up, but it is hard for he to fuck me doggy style, it really hurts sometimes) cause he is not very into the positions while I am topping. But I guess that position-wise, a couple can always find the ones that suits them best by trying all of them.
Aestheticly speaking, I do not like my curvature at all. As
@Ben Tramer said, an upcruved cock is sexy as hell, at least for me. My cock, being bent down, looks like it is always sad and droopy... it just does not give the same energy as a upcurved cock.