A new YouTube feature currently under test mode allows users to express their reactions without posting silly comments. They can just click one of the six buttons (LOL, OMG, EPIC, CUTE, WTF, FAIL) and instantly tag the video.
YouTube already highlights tags that use Internet slang words ("#LOL", "#FAIL", "#CUTE") from the comments and places links to a list of comment search results.
Google's blogging platform Blogger also has a similar feature, but it allows the blog authors to edit the list of reactions.
"With Reactions, readers can easily respond with one click, increasing feedback on posts."
[Thanks, Ron, Alex]