This is a really interesting question. Personally I have to go with "Sometimes", because let's be honest here, as soon as sex enters the picture you want to see it simply because you're are curious.
Well, at least this is what happens most of the time... but not always. A perfect example of when the use of sex, nudity and violence completely backfired was during when EA was trying to promote Dragon Age. I love BioWare games, hell they are easily one of my favorite developers, but after seeing all of those "sex & drugs n' rock n' roll"-styled commercials with Marlyn Manson it really made me less excited to play the game (...and bear in mind I had been looking forward to playing that game for years).
So in short, it really depends on what it is that you are promoting. If it's a hamburger, sure I'll probably look at it a little extra simply 'cause there's a half-naked chick on the poster (though if it's a naked Paris Hilton I'll have to gouge my eyes out with a fork afterwards) however if it's for a movie, a game or anything else for that matter that they want me to take seriously... don't do it. Seriously, just don't.