Over the past few months, several users pointed out that the submit button on the comment preview page wasn't working in Internet Explorer. It turns out that the cause is a bug in the comment rating module (you can read more about it here). I upgraded the module, but that seemed to introduce more problems than it solved. So now I've reverted to the comment rating module that has the comment preview bug. To get around the bug, you can copy the text from the comment preview form into a fresh comment window.