Dual monitor on an ati hd 3870, works fine until I reboot.
 

I have 3d effects working wonderfully, I even have catalyst control center which allows me to do dual monitors as one big screen,it works right away,until I reboot and then it reverts to mirrored. I can work with the one big screen but would really like separate desktops if at all possible, was able to do this in pclos2007 but am ready to try ubuntu.

You probably need to modify your xorg.conf

Section "ServerLayout"
...
Option "clone" "false"
...
EndSection

Or if you have my problem, adding -- -nolisten tcp to startx lets it start in the first place, when the network(wireless) isn't up.