Here's the setup:
Fedora 19, latest beta catalyst drivers (stable ones won't compile on latest kernel update), 2x 270x cards, 4x 24" widescreens, one on each of the two DVI ports on each card, arranged in a 2-over-two (square).
Using amdcccle, I can configure the two bottom monitors as one desktop across both. I can do this with the two top as well. The mouse pointer will move correctly around all four this way, but I can't drag windows to the top two. If I start a program on the top display with DISPLAY=:0.1; someprogram from a terminal, it will launch on the upper two-screened desktop, but the windows lack menu bars and the keyboard can never get focused, so you can't type in the upper windows. I don't want two "streched" desktops anyway - I want 4 desktops I can drag between - see below.
So, if I use amdcccle to configure the four monitors as 4 desktops, I can move the mouse correctly between them, but I can't drag programs around between them. Obviously, I need to enable Xinerama.... Which crashes the server before the log in manager loads.
So, the second situation is what I want, except I need Xinerama to work, except it doesn't.
Or am I going about this the wrong way?