After almost two weeks working with KDE 4.1beta, I decided to revert back to KDE3. There are certainly some problems to be expected for the beta release, including occasional crash of some applications. And I can make do with that.
The determinant is that I found myself often cannot use s2disk to save the current session for later resumption. That's very disheartening to me.I usually will not reboot my Debian GNU/Linux for months until I install a new kernel and want to run with it. That saves me a lot time rebooting the computer and bring all the applications up to their last state.
I'd keep using KDE 4.1beta if I reboot every day (if not each time I come to the front of my computer), as many users do.