I didn't realize until yesterday that I accidentally blocked everyone to add comments to my blog for a while. I was trying to reply to some comments and even when comments were enabled, the Submit button was not doing a postback. At first I thought it was because I changed my template and added a bunch of CSS overrides, but that was not the problem.
The problem (in case this is happening to you) is that I added a Technorati script to my blog. The script contains another form, so when the blog is rendered you have a form inside a form, and that's why a Submit button can't do postback.
Everything started working when I removed the script, so if you want to leave comments, you can do it now.
I apologize for the inconvenience,