Fedora :: F12 - Hangs At Random ?

About a week after I installed F12 on a brand new system, a friend came over and went on to play poker on facebook. At some point he yelled that the PC froze. I was working on another machine at the time and tried to ssh to the supposedly hung system, but couldn't; Except for playing poker he had audacious open and about 3 seconds of the song that was playing at the time of the hang, kept looping. Neither Ctrl+Alt+Backspace nor any of the Alt+SysRq combos had any effect whatsoever, so I had to press the reset button (and I have to say this was the first time I had to do so in linux after almost a decade of using it, save for a hiccup with my first gentoo kernel).

The system usually freezes if there are two or more sound streams, but that is not always the case. The best way to get the system to crash is by playing something in audacious or rhythmbox while seeking through a video in mplayer or vlc or having flash content appear in firefox (I am using adobe's latest 64-bit flash plug-in and have been using it without any problems -though on other systems- since F10). Also most but not all the times the system is going to hang, there are a few skips in audacious every ~10-30 minutes. I've been getting the lock-ups with every kernel released so far.

My system logs don't contain any useful info after each hang; there are however certain problems mentioned in syslog which I thought they could be relevant, but they always appear whether the system works fine or not, namely the following:

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I used to get a lot more of these with previous kernels:

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This one appeared every now and then until Dec 25:

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And this one is always there:

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Finally, at every boot I get this from abrtd, but it doesn't seem to be related:

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Yesterday, I devoted the entire day to hunting down the culprit, but I couldn't get the system to hang; I had rhytmbox, audacious, totem, vlc, mplayer and vlc all playing music and videos simultaneously from local disks, network shares and through upnp, I got myself a facebook account in order to play that zynga poker thing, I upgraded alsa-lib to 1.0.22 from updates-testing, rebooted countless times, but the system didn't hang nor did any of the above messages disappear.
Today as I was browsing through some web pages, one of which had an interactive flash ad, while listening to music and the system froze again.

System specs: