I've been having this problem for a while now; Debian Unstable 64-bit, Nvidia GTX560 for me.

Game update: AppID 440 "Team Fortress 2", ProcID 25398, IP 68.232.166.231:27015
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
Installing breakpad exception handler for appid(gameoverlayui)/version(1.0_client)
Installing breakpad exception handler for appid(steam)/version(1360966495_client)
Installing breakpad exception handler for appid(steam)/version(1360966495_client)
Installing breakpad exception handler for appid(steam)/version(1360966495_client)

qhull precision error: Only 4 facets remain.  Can not merge another
pair.  The convexity constraints may be too strong.  Reduce the
magnitude of 'Cn' or increase the magnitude of 'An'.  For example,
try 'C-0.001' instead of 'C-0.1' or 'A-0.999' instead of 'A-0.9'.

qhull precision error: Only 4 facets remain.  Can not merge another
pair.  The convexity constraints may be too strong.  Reduce the
magnitude of 'Cn' or increase the magnitude of 'An'.  For example,
try 'C-0.001' instead of 'C-0.1' or 'A-0.999' instead of 'A-0.9'.

qhull precision error: Only 4 facets remain.  Can not merge another
pair.  The convexity constraints may be too strong.  Reduce the
magnitude of 'Cn' or increase the magnitude of 'An'.  For example,
try 'C-0.001' instead of 'C-0.1' or 'A-0.999' instead of 'A-0.9'.
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
warning: Unknown nb_ctl request:  4
CShaderDeviceMgrBase::GetRecommendedConfigurationInfo: CPU speed: 3200 MHz, Processor: AuthenticAMD
GlobalMemoryStatus: 4294967295
CShaderDeviceMgrBase::GetRecommendedConfigurationInfo: CPU speed: 3200 MHz, Processor: AuthenticAMD
GlobalMemoryStatus: 4294967295
CShaderDeviceMgrBase::GetRecommendedConfigurationInfo: CPU speed: 3200 MHz, Processor: AuthenticAMD
GlobalMemoryStatus: 4294967295
warning: The VAD has been replaced by a hack pending a complete rewrite
Uploading dump (in-process) [proxy '']
/tmp/dumps/crash_20130218181659_1.dmp
success = yes
response:  CrashID=bp-1b47389e-69b4-4995-be97-83c462130218
/media/linuxGaming/Steam/SteamApps/robbiethe1st/Team Fortress 2/hl2.sh: line 72: 25398 Segmentation fault      ${GAME_DEBUGGER} "${GAMEROOT}"/${GAMEEXE} "$@"
Game removed: AppID 440 "Team Fortress 2", ProcID 25398 

I guess filedropper decided to remove the file. So here's another crash(they're quite frequent), this time on dropbox.

https://www.dropbox.com/s/5spxp4rgh6xlc0g/crash_20130220201235_1.dmp

My is kernel 3.5.7-1, if that's helpful. Also, while running tf2, the crashes are preceded by few second periods of looping/skipping sound(I guess CPU usage spikes? Some kind of local lag), seemingly at random, with anywhere from 10 seconds to a few minutes in between them. After a few such lag/skipping spikes, or sometimes on the first one, the spike will end in a crash.