Like I already said before, openSUSE 12.3 was released today, and I’ve done the usual live upgrade with zypper.
The upgrade itself worked without any problems, and the resulting installation was usable without issues right from the start.
I logged into KDE 4.10 and everything that I’ve tried works just fine. I admit, I can’t say anything about performance as my test machine is accessed via a NoMachine remote desktop session.
After that I upgraded the KDE 4.10.0 to 4.10.1 from the opensuse build service, and that also went well and posed no problems afterwards. Now I’m waiting for my own repository for 12.3 to rebuild against KDE:Release:410.
I’m pretty confident in saying that with 12.3 the process of a live update via zypper can be done without major fear, as long as one has ones repositories set up properly, and with the right priorities (packman and KDE from OBS should have a higher priority than the stop openSUSE repositories).