KDE 4.0 is here, and it looks pretty good. On the lottalinuxlinks podcast #59, Dave Yates interviewed Rich Johnson, a contributor to Kubuntu. Since Kubuntu uses KDE, Rich has experience through the development cycle of KDE 4. Rich indicated that the average user should probably wait for KDE 4.1.
I'll probably load up one of the more powerful Free Geek computers up with Kubuntu when KDE4 is integrated, and see how it feels.