Folks, I apologize for this and do not fully understand it, but:
At least half a dozen times in the last two days, I’ve approved a comment from in the middle of a long list of spam comments, then deleted the rest, only to find that the approved comment never appears. My best guess is that internet latency is fighting with the Ajax-y code that WordPress uses in the comment moderation queue.
The result is that 6-10 thoughtful, welcome comments have been nuked from the moderation queue. If you are one of the victims, please don’t take offense. I’ll try to slow down and make sure that the bit gremlins don’t eat any more comments in future.