I used to have Blogger comments. Then I switched to Haloscan, and all of my old comments got hidden. Haloscan no longer exists, and they want me to transfer my comments to some paid service, which I am not going to do. So I uninstalled it and now the original Blogger comments are back, but any comments left through Haloscan are gone. I almost decided the blog wasn't worth this headache, but it turned out not to be so bad.
The bad news is, Blogger doesn't always give me an email address so I can reply to comments. The good news is, I'm really bad about replying to comments, anyway, and now I have an excuse.