This is just in the testing phase right now, and doesn't seem to be an option for all users, as I can't seem to find the feature when I post a status update. Facebook is testing different price points as well, and a spokesperson said that they may not even charge at all, though I don't know if that means they'll just cut the feature entirely or highlighting a post will cost through different means.
This featured would obviously benefit companies and individuals promoting their work more than those using the site just to stay in contact with friends. That being said, I'm sure I could get a lot of amusement out of highlighting my most inane posts.
via Slash Gear