I did. The weirdest bug ever. Turns out it was the atheros card fault. The machine was more or less stable with a ping running in the background. Otherwise, it would crash - several times a day with 32 bit userland binaries, once every 2 days with 64 bit userland binaries. Like you, no log message - regardless of what log system I used, or even remote logging.
I checked so many things it took me several month to figure it out -- and since none of the recommended atheros kernel options helped, I could fix that only by replacing the card with a apple branded atheros - ar9380 if I remember correctly.
Try to remove all tthe ath9k modules and use your computer as you normally do. See if you have any crash.
BTW I was also having opengl related freezes (100% reproductible with xlock), fixed by adding NoDRI to xorg.conf