... when I read a post and go "hmm, I wonder what people had to say about this" or "oh, I've gotta make a comment on this" and click through to find that it no longer exists. The post has been erased from history (but not from my news reader). And then I feel kind of guilty about having read it, since clearly the author changed their mind about having had it public in the first place...

(And somehow it's always one of two or three people... what is it with you and your post-and-delete habits?)