I think it happens almost as often as it does for women, but most people don't really care or think it's that big a deal. So much that most probably don't even notice it happening right in front of them.
And to be honest, I think men can be objectified even if they aren't the focus, when things are done to women in media that is obviously meant to target men. Such as the Game of War commercial that has Kate Upton in it. There is only one reason she is in the video and we all know it. Sure, in a way she is being objectified but it's relative. She's being paid for it and she chose that life for herself where such a thing is in a sense, required.
While playing Mass Effect 2, there were several camera angles that blatantly were focused on Miranda's ass. Yes, nice bum and all, but that was the sole purpose of the angle. Not because it was just the right place to put it for the situation. The fact that it was directed at me as a hetero male gamer slightly annoyed me.
Men's brains react when they see women, I think much more so than when a woman sees a man, and the fact that so much advertisement and media is designed to target that biological fact. I find a bit objectifying.