I've learned the hard why today why logs are uberuseful (once again) and that RSSH is a pain to debug if you're having trouble with it. For future reference, check '/var/log/messages' as the first thing you do when having trouble with SSH, especially RSSH.
For those not in the know, RSSH stands for Restricted Secure SHell, and is very useful if you want to create jails for people who have to transfer files between their boxes and your server. However, it's very hard to debug because when you log in, you don't get any messages, you either get the "This is a an account restricted by RSSH" message or you get the ever so friendly and useful "Connection closed" message. As it turned out, the passwords for several of my users had expired today and this created a huge issue when they weren't able to upload batch files to our server. After spending just over an hour finding that the problem was related to SSH login, I received a very helpful message from one of the people who operates our server showing me a grepped slice of the /var/log/messages log saying that the password had expired for several of the users : coincidentally, the only users that I had tried troubleshooting the problem with.
The point of all this: check '/var/log/messages'.
*EDIT:* Today is officially known as Bad Monday for me.