My biggest annoyance with Disqus is that you can't tell in advance what requirements it will make in terms of signing in. Some sites have openid and some don't, some are okay with anonymous comments and some aren't. Usually you have to type some junk, hit post and then find out what you'll be allowed to use and give up, or comment as appropriate. Sometimes I forget, write an insightful comment and then find I can't actually post it.