When I use LightDM, it will auto-login to desktop just fine. The only problem is Compiz doesn't work, and menus don't work. I can't right-click the desktop, and I can't select program menus in the top bar (I.e clicking "File" does nothing).
When I use GDM, I only get a blank blue screen and the mouse cursor. I can't Ctrl+Alt+Backspace to restart, but I can Ctrl+Alt+F1 and Ctrl+Alt+F7 to switch modes. I don't think it's auto-logging me in, but I'm not sure. It plays the login screen noise.
Will update with more information when I get home!
EDIT: Okay, so I did a fresh install, just to ensure I hadn't borked something playing in the console. I reconfigured my setup as I did before, with the same results.
The only difference is that instead of setting "vga=normal nomodeset" I set "GRUB_GFXPAYLOAD_LINUX = text". Also I only have the DisplayLink monitor configured in my xorg.conf file.
At this point I'm using the open radeon driver, although I used the proprietary ati driver before.
I'm not sure if I'm having a problem with: - X configuration - Graphics driver - DisplayLink driver - Unity - LightDM - Compiz - Or something else
The resolution of the monitor is 800x480, 16bit. I tried setting a larger virtual resolution of 1200x720 (because the real resolution is lower than the recommended resolution), but it causes Ubuntu to boot into low graphics mode. When I get home I'm going to install the fglrx driver and see if it enables virtual resolutions, which may further enable my window manager to function properly.
EDIT2: Just discovered the concept of composite rendering. I'll try disabling that in xorg.conf too.
EDIT3: Why isn't this working? If you need to see a file or log, let me know.