This is my setup:

*AMD Radeon 6870, latest fglrx from AMD website
*3x BenQ 21" monitors, 1920x1080, two on DVI, one on MiniDP->DVI.
*Debian Sid.
*GNOME 3.x (latest in Debian Sid repo tested extensively)

My issue is this: I have the 3 monitors as a single desktop. I wish for the Gnome Panel to be on the center monitor, like this:

     | Panel |
Blue |  Red  | Green
     |       |

In the "Displays" options, by default the black bar representing that is on Blue, which gives me:

Panel |       |
 Blue |  Red  | Green
      |       |

However, as soon as I move the black bar to another monitor, buggy things start happening. 

If I set it to Red and apply, the panel remains on "Red", but the position of the Red and Blue monitors in the dialog switch [so Red|Blue|Green with bar on Red], even though they're still "in line" [Blue|Red|Green] in terms of the virtual workspace; in short, nothing actually changes. I also lose my mouse (I can't see it or move it around) on the two monitors that have changed. Logging out results in the settings reverting to how they were.

If I disable the Blue monitor, the bar moves to the Red monitor as desired. Same if I disable the Green monitor and *then* switch them. But as soon as I enable the third monitor, it's back to square one.

I also have issues (at least, pre-reinstall that I did last night) with the desktop environment flickering and blinking on and off. I can't tell if this is a problem with Gnome or something deeper (X, fglrx?) however.

This is my first bug report so I hope I've been clear. Any advice would be appreciated; GNOME3 is the only DE on Linux that I've found to meet all my needs and I'd like to keep using it, but for me this issue is basically a deal breaker (my monitors are positoned in a way that makes life very difficult if my panel is on the leftmost monitor).