I've now been running the beta pretty well exclusively since it came out. Working well, with only a few oddities to report.
Brasero, set to generate and test an image checksum complains about being unable to eject the media at the end of testing the burnt image.
Seamonkey 2.1b2 is not completely backward compatible with 2.0.x - bookmark storage has changed, so going from 2.1b2 to 2.0.12 and then back to the beta loses all the bookmarks.
Not too important....
Cmake produces a menu entry, but will not run the gui - missing a libQTGui library.
The update notifier is behaving a bit strangely - it will appear in the system tray, but when opened, Gslapt reports no updates available. Has happened several times. I am running my own MC build (220.127.116.11), so I've blacklisted MC - I wondered if that might be causing the odd behaviour, but can't think of any way to really check.
Other than those items, the beta has been rock solid, running really well. I also like the new login screen graphic - very nice.
Must get round to installing the 64-bit version as well.