Apparently, Google is taking over Blogger, which is ultimately going to be a good thing. They're still ironing out bugs in the transition though and unfortunately, I agreed to switch over before everything was resolved. That affects not just this blog, but also any group blogs that I've created, so I apologize for the frustration.
I'm trying to figure out how to ask questions directly of the Beta team, but in the meantime, I found this unresolved issue in Beta's Known Issues log:
Logging in with an old Blogger account to post a comment on the new Blogger is giving a “please try again later” error. Until we fix this, it may work to log in first at http://www.blogger.com/login.g, and then go to the comments page on the new version of Blogger in beta.
I also understand that folks are having trouble commenting even anonymously, but I haven't found anything about that amongst the Known Issues. I'll keep looking for a way to communicate directly with the people in charge.
In the meantime, thanks for your patience and please keep letting me know what kind of problems you're experiencing.
Update: Someone was able to comment on the Constantine post, so it looks like it may be an issue with old vs. new Blogger accounts. The new Blogger accounts are actually Google accounts, so if anyone who's been having problems is interested in signing up for one (if you have a Blogger blog, you're eventually going to have to anyway), I'd be interested in seeing if that solves the problem for you.
Also, I just thought of another workaround. This blog is syndicated on LiveJournal, so if you want, you can always comment there.