Yesterday on my Mint 15 KDE (64 bit) system, I managed to hang up Firefox by attempting to play a video on a Tumblr site. Okay, not impossible. But it also crashed Kwin - window decorations gone as well as the taskbar. S#!t happens, I guess. So Ctrl-Alt-Backspace, and back to the login prompt (using kdm - I don't like the new html login). When I logged back in, still no window decorations. The taskbar shows up, but without my selected theme. Repeatedly.
After rebooting the system, everything's fine. But I'm pretty surpised that an application can bring down kwin so dramatically. Does that surprise anybody else?