I recently upgraded to Saucy and things were going fine. I needed to do a full restart so I did so (from a KDE Plasma desktop).
After restarting I am unable to log in to a desktop session on my main account (will).
Doesn't seem to matter what type of session I select - Kubuntu, Plasma, Xubuntu, Ubuntu (Default) - none of them work.
In all cases, after typing my password and pressing Enter, the screen goes black momentarily, and then I am back at the login screen. There are no error messages or anything.
I am still able to do stuff requiring superuser privileges via the console (CTRL+ALT+F1).
The "guest session" option works fine.