I have found that KDE 3.5.9 with OpenSUSE 11.0 is the most productive and trouble-free environment. I have another partition with KDE 4.0 (and soon to be 4.1 when the dependency problems on x86-64 are sorted out) but that is just for experimenting. Even KDE says the 4.1 is for early adopters and casual use and that production use should wait for 4.2.
From the release announcement:
While KDE 4.1 aims at being the first release suitable for early adopting users, some features you are used to in KDE 3.5 are not implemented yet.
The devs state that KDE4 has been included in Suse to aid development. It’s not ready for the mass market yet. But you have years of experience, so if you want to help, you might install it as a philanthropic gesture. But you wouldn’t IMHO do any critical work with it.