As I already reported, ATI has new drivers available for Vista build 5308. Now I’ve tried them and the result is, well, mixed.

Pro Con
I can now switch resolutions. The native resolution of the display (1680x1050), which used to be the only one available apart from 640x480, is now the only one that is not available. Trying to switch to it results in a switch to 640x480.
I can now run the ATI control center and there’s a wonderful clone screen funtion there for the external display. It doesn’t work - extending the Windows desktop to the other screen works (like it did before), but the cloning bit doesn’t. Every time I try to activate it, the external screen is deactivated.
Many of the old boring drawing issues are gone. Some of them have been replaced by interesting new drawing issues. For example, the round blue button of the start menu vanishes under the glass task bar sometimes, which it never did before the driver update.

Not sure yet if I regard this as an overall improvement… I’ll go with it for a while and see how I like it.