I thought I would post to let everyone know how to fix a problem I noticed many users seemed to describe but no one seemed to have an answer to. The 'name' and 'email' form box wouldn't show up and when users entered a comment in the comment area and hit submit they would get an error message - name and email required!
This drove me nuts and I couldn't rectify it despite upgrading WordPress and doing a reinstall and re-reinstalling comments.php and many related things I saw suggested that seemed even remotely related. Fortunately for my n00b self, I ran into mention of a blank user causing someone else similar problems.
I don't know why this works or what it means, but it worked and doesn't seem to cause any problems. Where the 'name' and 'email' boxes should have been it said 'Logged in as [blank].' In the admin panel, go to users and simply give the blank user with the email address 'firstname.lastname@example.org' a nickname. Any name.