I was just looking at a friend's modestly funny entry from earlier in the day, which I noticed had received no comments. I didn't think it deserved to be ignored, and went to comment. And drew a blank. And then I suddenly realized what LJ needs:
An 'ACK' button
Just a button that I could have pushed that would tell my friend "Yakshaver read your post and wanted you to know in some vague inarticulate way that he approves."