What is this youtube? A like button would make things needlessly complicated. Its easy enough to tell how people feel about a manga because too many people give just 10s and 1s on everything. I would disagree with this idea.
A "thankyou" button or like button for each post would be a very good feature to add. Are admins able to do this? or has it been tried before but made things worse? I think it would promote more discussion and activity. People want to be thanked/liked for contributing their time of posting to this site.