As said so many times, if it's a part of the story, and is done tastefully and mature, even a fully covered sexual act wouldn't bother me.
However, then you have games like Red Alert 3, where Tanya is reduced to a blond bimbo from the kick-ass brunette she was in the previous games, and Natasha is dressed like a bad whore. That's done baaad. Way too much emphasis on 'sex sells' <.<
Damnit EA, if I wanted bare thighs and bellies, I'd watch porn instead.. I wish they kept meaningless sex appeals out of it, and kept it all about the whacky, out-of-proportion war between the Soviet Union and the West (Also kicking the Japanese out of the story, I for one never cared for them)