So, I've spoken to the kind folks at #radeon on irc.freenode.net. My card (Radeon HD 7850M) is supported, but only with Xorg 1.12 and lower so I've downgraded it and its dependencies. HOWEVER. As has always been the case, any attempt to switch from the integrated card (Intel 4000) to the discrete card causes the system to hang (whether at boot, after starting and stopping X, via a delay (DDIS > vgaswitcheroo/switch), anything). It is still responsive (e.g beeps when I scroll past the buffer, restarts on a ctrl+alt+del, ...), but the display freezes on the most recent screen. I'm not even sure which log to look at for this. Anyone want to request some information or help?