Recently I'm finding that some Mac OS X applications are crashing frequently with backtraces like the following:

Process:         Mail [39226]
Path:            /Applications/Mail.app/Contents/MacOS/Mail
Identifier:      com.apple.mail
Version:         4.4 (1082)
Build Info:      Mail-10820000~1
Code Type:       X86-64 (Native)
Parent Process:  launchd [338]

Date/Time:       2011-01-12 21:59:48.383 -0500
OS Version:      Mac OS X 10.6.6 (10J567)
Report Version:  6

Exception Type:  EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000
Crashed Thread:  12  Dispatch queue: com.apple.root.default-priority

[...]

Thread 12 Crashed:  Dispatch queue: com.apple.root.default-priority
0   com.apple.CoreFoundation        0x00007fff81653975 __THE_SYSTEM_HAS_NO_PORT_SETS_AVAILABLE__ + 5
1   com.apple.CoreFoundation        0x00007fff815a1f69 __CFRunLoopFindMode + 553
2   com.apple.CoreFoundation        0x00007fff815a1c5d __CFRunLoopCreate + 317
3   com.apple.CoreFoundation        0x00007fff815a1a78 _CFRunLoopGet0 + 744
4   com.apple.CoreFoundation        0x00007fff815dc90a CFRunLoopRunInMode + 58
5   com.apple.MessageFramework      0x00007fff81d01183 +[NSRunLoop(MessageExtensions) _flushQueuedEventsAddingSource:] + 120
6   com.apple.MessageFramework      0x00007fff81d010d2 +[NSRunLoop(MessageExtensions) flushQueuedEvents] + 36
7   com.apple.MessageFramework      0x00007fff81ce6515 -[_MFInvocationOperation main] + 275
8   com.apple.Foundation            0x00007fff83921de4 -[__NSOperationInternal start] + 681
9   com.apple.Foundation            0x00007fff83a00beb __doStart2 + 97
10  libSystem.B.dylib               0x00007fff801402c4 _dispatch_call_block_and_release + 15
11  libSystem.B.dylib               0x00007fff8011e831 _dispatch_worker_thread2 + 239
12  libSystem.B.dylib               0x00007fff8011e168 _pthread_wqthread + 353
13  libSystem.B.dylib               0x00007fff8011e005 start_wqthread + 13

[...]

Any ideas about what might be causing this and/or how to remedy it?