This is why I don't comment on many front page memes. Late comments don't really get much attention.

I almost always read ALL the comments, and up vote if it warrants it. I do enjoy helping a comment get more upvotes than the actual meme too, I'm kinda mean that way.

That's not really a hard-and-fast rule. It really depends a lot on the type of comment it is. I've commented on memes when there are already lots and still sometimes get good responses. On the other hand sometimes I've commented on memes where I'm the only comment and nothing happens at all.

Well, late comments rarely start conversations as good as early comments. Well, at least in my experience.