I’m running KDE4 RC1 as my main desktop for 2 days now. Only few crashes, so productivity is good. But there are many small bugs. And it’s not very fast/responsive. But this is at least partially to blame on all the debug code.

Quite happy so far! It’s shaping up! Please test!!!

Packages from Kubuntu: HOWTO
KDE Four Live: openSUSE based Live CD
KDE4Daily: full virtual machine image with efficient update mechanism to SVN head

Please report any possibilities to try out KDE4 the easy way in the comments section:-)