Had this happening all day on exit from Steam:

john@joran ~/Steam/SteamApps/common/Half-Life > Shutting down. . .
/home/john/Steam/steam.sh: line 341: 17764 Segmentation fault (core dumped) $STEAM_DEBUGGER "$STEAMROOT/$PLATFORM/$STEAMEXE" "$@"

Running in gdb:

Shutting down. . .
[Thread 0xee460b40 (LWP 18810) exited]
[Thread 0xee35fb40 (LWP 18811) exited]
[Thread 0xe000db40 (LWP 18835) exited]
[Thread 0xedeffb40 (LWP 18812) exited]
[Thread 0xef8b0b40 (LWP 18807) exited]

Program received signal SIGSEGV, Segmentation fault.
0xf7c0d175 in ?? () from /lib/i386-linux-gnu/libc.so.6
(gdb) 
(gdb) 
(gdb) bt
#0  0xf7c0d175 in ?? () from /lib/i386-linux-gnu/libc.so.6
#1  0xf7c0e22f in ?? () from /lib/i386-linux-gnu/libc.so.6
#2  0xf7c10ddc in malloc () from /lib/i386-linux-gnu/libc.so.6
#3  0xf7e07627 in operator new(unsigned int) () from /usr/lib/i386-linux-gnu/libstdc++.so.6
#4  0xf7e0774b in operator new[](unsigned int) () from /usr/lib/i386-linux-gnu/libstdc++.so.6
#5  0xf4aff436 in CreateEvent(void*, int, int, char const*) () from /home/john/Steam/ubuntu12_32/libsteam.so
#6  0xf48e9d26 in common::CBlobRegistry::CBlobRegistry(std::string const&, bool, unsigned int) ()
   from /home/john/Steam/ubuntu12_32/libsteam.so
#7  0xf491cd93 in (anonymous namespace)::RegistrySingleton(bool) () from /home/john/Steam/ubuntu12_32/libsteam.so
#8  0xf491cf23 in Grid::CClientRegistry::Instance() () from /home/john/Steam/ubuntu12_32/libsteam.so
#9  0xf49fd36e in Grid::CSClient::CDownloadRateEstimator::ReportStatistics() ()
   from /home/john/Steam/ubuntu12_32/libsteam.so
[#10](/issue/ValveSoftware/steam-for-linux/10) 0xf4a16af4 in Grid::CSClient::CService::~CService() () from /home/john/Steam/ubuntu12_32/libsteam.so
[#11](/issue/ValveSoftware/steam-for-linux/11) 0xf4a16da9 in Grid::CSClient::CService::Cleanup() () from /home/john/Steam/ubuntu12_32/libsteam.so
[#12](/issue/ValveSoftware/steam-for-linux/12) 0xf49f6b07 in Grid::CSClient::Cleanup() () from /home/john/Steam/ubuntu12_32/libsteam.so
[#13](/issue/ValveSoftware/steam-for-linux/13) 0xf4add610 in SteamShutdownEngine () from /home/john/Steam/ubuntu12_32/libsteam.so
[#14](/issue/ValveSoftware/steam-for-linux/14) 0xf4abc11d in (anonymous namespace)::CSteamInterface006::ShutdownEngine(TSteamError*) ()
   from /home/john/Steam/ubuntu12_32/libsteam.so
[#15](/issue/ValveSoftware/steam-for-linux/15) 0x08067492 in RunSteam(int, char**, bool, bool) ()
[#16](/issue/ValveSoftware/steam-for-linux/16) 0x0804fc72 in main ()

Processor Information:
Vendor: AuthenticAMD
Speed: 3199 Mhz
4 logical processors
4 physical processors
HyperThreading: Unsupported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Supported
SSE4a: Supported
SSE41: Unsupported
SSE42: Unsupported

Operating System Version:
Ubuntu 12.04.1 LTS (64 bit)
Kernel Name: Linux
Kernel Version: 3.2.0-36-generic
X Server vendor: The X.Org Foundation
X Server release: 11103000

Video Card:
Driver: NVIDIA Corporation GeForce GT 630/PCIe/SSE2
Driver Version: 4.3.0 NVIDIA 310.14
Desktop Color Depth: 24 bits per pixel

Miscellaneous:
UI Language: English
LANG: en_GB.UTF-8

Recent Failure Reports:
Thu Jan 24 19:38:59 2013 GMT: file ''/tmp/dumps/crash_20130124193835_1.dmp'', upload yes: ''CrashID=bp-295ac786-442e-4ab2-a6c8-4a43c2130124''
Thu Jan 24 22:32:32 2013 GMT: file ''/tmp/dumps/assert_20130124223157_1.dmp'', upload yes: ''CrashID=bp-b6124383-269f-4c18-a7d0-7cd842130124''
Thu Jan 24 23:12:26 2013 GMT: file ''/tmp/dumps/assert_20130124231134_1.dmp'', upload yes: ''CrashID=bp-4f5cc826-a3ab-4d5f-95bb-32ef42130124''