TL;DR: Here the problem was apparently caused by an issue (most probably some obscure race condition) between OpenGL and KWin.
To workaround it, one must disable OpenGL and use XRender instead (in System configuration > Desktop effects > Advanced > Compositing type, select "XRender" instead of the default OpenGL).
A few desktop effects will not be available anymore, but at least the system will be stable and not freeze anymore.
Long story:
The issue occurred every few weeks randomly, some times several times a day, some times two or three weeks with no issue, and was therefore quite difficult to analyze (BTW at some point I switched to another video card, switching from radeon to Intel i915 without any impact on the issue, therefore it is related neither to the graphic card nor its driver).
I left a script running in the background and doing automatic checks every three minutes in an infinite loops so they could hopefully catch something when the desktop freeze.
Indeed, the freeze can be programmatically detected through qdbus, and in particular this call fails if and only if the desktop is frozen:
qdbus org.kde.Kwin /App org.freedesktop.DBus.Peer.Ping
While normally it has no output and a return code of 0, when the desktop is frozen this command fails with a return code 2 and a "NoReply" error message.
For information, I've also checked the status of org.kde.plasma-desktop, org.kde.kuiserver and org.kde.kded which all seem sane when a freeze occurs, therefore KWin seems the real culprit.
I tried several ways to restore the desktop environment integrity with no luck. Trying to restart KWin cleanly using kquitapp kwin or kwin --replace didn't seem to have any noticeable effect. I tried to kill and rebuild the complete desktop environment as follow:
kbuildsycoca4
kquitapp plasma-desktop
kquitapp kwin
kquitapp kuiserver
sleep 2
killall plasma-desktop kwin kuiserver; sleep 2
killall -9 plasma-desktop kwin kuiserver; sleep 2
kstart kuiserver
kstart kwin
kstart plasma-desktop
The desktop unfreezed itself! ... but only for one frame: the screen (as can be seen when looking at the clock in the taskbar) is updated and freezes immediately again.
Nevertheless, having found the culprit, I've found an old "high, critical but won't fix because too obscure" issue here. Same symptoms, same diagnostic steps, and finally this suggested workaround: use XRender instead of OpenGL.
It has been several months now since I applied this change and I encountered no freeze since then, so I think this workaround to be correct for this issue.
Best Answer
I scoured the web, following every suggestion I could find to get integrated Intel HDA audio to work under Fedora 17. Nothing worked until I stumbled across this little gem:
Add your user to the 'audio' group, then rebootFrom a shell prompt:
After that, all I had to do was go to the Mixer control panel and select 'Playback: Internal Audio Analog Stereo (PulseAudio Mixer)'.