I think its kind of redundant. There's no point in having both....as the current THANKS system essentially gives people 'points' for getting thanked for making a useful post while noting that a post was deemed useful. It seems like the only thing different about the LIKE system is that it can be tracked and sorted.
Ideally, you'd only want one system. If there was a way to port over all the thanks into the likes system and display LIKES in the user profile, that would be great. Or, if the THANKS system could be modified to be similar to the LIKES system so that threads could be sorted by THANKS. I don't think that having both is the solution because it makes both systems less effective as some people will LIKE and some people will THANK, and in the end what you really want is everyone doing one or the other to get a true reading.