I think the like button would be fine, except for the fact that the likes are tallied. The only reason to count the number of likes is for comparison, at which point it becomes a popularity contest. Popularity contests enshrine the winners and alienate the losers. The question is, do we need to know who is the most liked contributor?
If thats really important, just look to see who's threads have the most views. It won't tell you if they are liked or loathed, but you will know who garners the most interest. Personally, I value a persons thoughtful contribution, over their clicking an approval button.