A commenter wrote (by email):
I’ve noticed that you’ve quit approving my comments on your blog. I hope I didn’t anger you in some way or write something you felt was inappropriate.
I have not been unapproving any comments. If you have comments that have not appeared, they have probably been going into the spam filter. I get literally thousands of spam comments a day and so anything that hits the spam filter is gone forever. I think there is a way to register as a commenter; that could help.