Very strange and very annoying problem.
I'm running 3 * 1920x1200 eyefinity, using both mini displayports and the DVI port from my 7970.
I also have a Smyth A8 Realiser (think of it as a reciever or audio device) that is connected via HDMI and extended.
Everything works correctly as Eyefinity + extended desktop, but if I shut off my monitors and turn them on again they all display the same 1920x1200 screen. Catalyst control center says that there is an eyefinity display group made of all three monitors, but won't let me set the resolution higher than 1920x1200. In order to get eyefinity working again I need to disable the eyefinity display group and create it again from scratch. Having to do this every time I turn my monitors on is hugely annoying.
The weird part is, if I just restart my computer without turning the monitors off eyefinity doesen't need to be recreated. If I don't have the Realiser connected then eyefinity is persistent when I turn my displays on or off.
I'm currently using Cat 12.11 Beta 11, but the same problem persisted in Beta 8, running Windows 7 Ultimate and my montiors are HP LP2475w's.