I had total failure with beta kde4 using Mandriva 2008.1 and now I have gone to Kubuntu 8.04 Hardy Heron. Things are much better but I still had issues with my kicker (taskbar) disappearing.
After a little Googling I found a site with a resolution. Restart plasma.
I wrote this little script as a quickie, in case it is a recurring problem.
Go to the following link:
I didn't take the time to package it under GPL and what sense would that make. These problems will be resolved soon enough, but either way do what you want with it...gather your friends in a circle and laugh at it, use it, modify it, burn it whatever rings your bell.
Hope it helps someone