I was thinking saving to PDF would be really useful using this:
I think bookmarks would be another really useful feature so you can save other people's code.
Here's the list that I have come up with so far. I don't know if these have been implemented or not. Some of the ideas probably aren't very good or necessary but eh...
-Add notes/message to correction
-Email user password if they forgot
-Login and extend the life of a previous post
-Ability to upload a file
-Spam control, maybe just enter a number and do a simple cipher like adding one to make sure the hidden field isn't being used
-Show the number of views per post
-Show statistics on database usage and total stats
-Translations to other languages
-Email code to user (potential spam issues here)
I'm pretty busy this week but I'll see if I can get some time this weekend to look at the code.