I would say the the biggest value of CodeBrag is that it is a well designed tool that does one thing well; such tools are usually worth their price - at least for the time they save not fighting other tools. Or writing on IM :)
Besides, how often do you say to others that you liked their code? The simpler that is, the more often people will do it.
I've never found myself wanting a like button for code. It's a nice gimmick, but I don't see it providing enough value that would impact my decision to use a product providing it.
It's not all about this "Like" button. There are other things in Codebrag we think can make it worth trying: all your duties in one place (commits waiting for your review, comments and likes from other users you may want to reply to). Also it doesn't stand on your way, no tons of clicking, going through complicated lifecycles and so on.
Besides, how often do you say to others that you liked their code? The simpler that is, the more often people will do it.