Originally Posted by Unforgiven
In longer threads it will highlight the useful posts, but I see your point. Maybe something like "Helpful Post."
I see this a "thanking" the post. I may be the dumbest person on a thread so my 2k+ thanks are meaningless, but a really good post in a root thread by a new user with 20+ likes will stand out. Especially with the link at the top that ranks the liked posts.
Just like thanks are an easily visible way to judge a user's contribution as a whole, likes are an easy way to judge a post's or thread's contribution.