Just a quick heads-up: I’ve just uploaded mesa 7.10.2-4, which is multiarch-enabled, thanks to Steve Langasek. As explained in its changelog, this breaks the X server currently in testing and in unstable, but a rebuild is already pending, which will make everyone upgradable.

For curious people, those commands took care of scheduling the binNMU, with a proper dep-wait:

wb nmu xorg-server . ALL . -m 'Rebuild against new (multiarch-enabled) mesa.'
wb dw xorg-server . ALL . -m 'libgl1-mesa-dev (>= 7.10.2-4)'

In the meanwhile, if your mirror gets a new mesa without the rebuilt server, your package manager should bail out and refuse to upgrade mesa (or propose to remove the server). So wait a bit, upgrade everything, and enjoy!

mesa 7.10.3 (released a few hours ago) should reach unstable tomorrow, so that we can ask our users to track (possible) regressions between 7.10.2-3 and 7.10.3-1 to either 7.10.2-4 (multiarchification), or to 7.10.3-1 (the stable upgrade), thanks to the excellent http://snapshot.debian.org/ service.