I tried KDE on several different occasions this year, and each time the bottom panel froze on me when trying to configure it, usually within the first minute or two. It felt a bit like I was still using KDE4 when it was first released.
I think I've had some panel hangs up until a couple of months ago. It was usually some tray plugin (happened after particular changes in the network or sound system configuration) or multi-screen configuration change related. In any case, the workaround for a hanging or spazzed out desktop shell is: open krunner (it's a different process, should still work) and run plasmashell --replace.
