I reflexively downvote people who do that. It's an extremely jarring abuse of the English language, and furthermore, serves absolutely no purpose, as jgrahamc points out, on a site with the possibility to either simply upvote, or comment in a more meaningful way.
As an alternative, try something creative like "I completely concur with the spirit of this comment, and would like to add ...." or "The sentiments expressed within the above comment could not be more clearly or intelligently stated. Furthermore ...", or, say, "Quite right, ..." or... well, pretty much anything that's not just the regurgitation of a boring meme.