I'm really not sure if this is a problem with VO or with my video driver, but since the conditions that trigger the bug are very specific, I figured I'd post it here.

A freeze may occur just after login when the station interface appears or just after docking. It never happens when flying or undocking. It seems more likely to happen when I first log in than after playing for a while.

The UI becomes completely unresponsive, and attempts to kill X or switch to a TTY have no effect. I can ssh in from another machine and kill VO, restart X and generally poke around, but it has no effect on what's visible on my screen. VO remains until I reboot the computer, which must be done via SSH or a hard reboot.

Technical information:
Distribution: Ubuntu 9.04
X server: X.org server 1.6.0 (X.org 7.4)
Video card: mobile FireGL v5200
Driver: X.org Radeon driver 6.12.1 (ATI's proprietary fglrx driver performs better, but it doesn't support this card and X version because a 2-year-old high-end card is now "legacy")

Confirmed that this is driver-related. I spent two days splicing the X server from Ubuntu 8.10 in to 9.04, finding the combination of fglrx and kernel versions that would work, figuring out why /dev/dri/card0 wasn't being created automatically, determining why X was using 100% of a CPU core and trying out suspend/resume hacks.

The result is a working R500-series GPU with fglrx on Ubuntu 9.04, complete with painfully slow and sometimes unreliable suspend and resume - just like fglrx ought to be. VO hasn't frozen since.

Somebody remind me to go with nVidia next time.