For me the issue is different to yours. Like you I am also using the KDE4:UNSTABLE, but I have seen this problem already some time ago when the 2.6.29 version got in the KOTD location. Kernel 2.6.28 worked fine, but the issue started already once the 2.6.29-rc3 became available. I can start whatever program without any problems and I have been working the whole day without any issue. Unfortunately at a certain moment I had to switch to the console to perform some tasks and once switching back I noticed that the whole desktop is hanging. I can move the mouse, but that is it. So I can not move back to a console to kill kwin and then to try again.
However I just tried something else. I switched off the Desktop Effects in KDE4 and rebooted the PC with the 2.6.29 kernel. With these settings I can now change to a console session and back again, without any issues. What I notice however is that when I switch back with Ctrl-Alt-F7, I shortly see the graphical screen with the top covered in black (about half a second), then the monitor switches to powersave mode and half a second later the correct graphical screen is displayed again. So somehow the Xserver is doing something here what causes the hang-up if the desktop effects are enabled. Maybe it is the composite mode that is either enabled or not ??
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