10.4 Authentication stops working

After 30-some days of uptime since I last saw this problem, authentication seems to be broken on geeklair.net again (and will be until I can get someone to reboot the machine).

It looks like things are getting stuck inside the security server, here's a sample from mutt getting stuck:

Analysis of sampling pid 19227 every 10.000000 milliseconds
Call graph:
985 Thread_0f0f
985 start
985 _start
 985 main
  985 mx_open_mailbox
   985 libintl_dcigettext
    985 _nl_locale_name_default
     985 CFLocaleCopyCurrent
      985 __CFApplicationPreferencesCopyCurrentState
       985 _CFStandardApplicationPreferences
        985 CFNotificationCenterAddObserver
         985 _CFXNotificationRegister
          985 __CFGetSessionIDString
           985 __CFGetSessionID
            985 SessionGetInfo
             985 Security::SecurityServer::ClientSession::getSessionInfo(unsigned long&, unsigned long&)
              985 Security::SecurityServer::ClientSession::activate()
               985 Security::ModuleNexus::operator()()
                985 Security::ModuleNexusCommon::create(void* (*)())
                 985 Security::ModuleNexus::make()
                  985 Security::SecurityServer::ClientSession::Global::Global[unified]()
                   985 ucsp_client_setup
                    985 mach_msg
                     985 mach_msg_trap
                      985 mach_msg_trap

Total number in stack (recursive counted multiple, when >=5):

Sort by top of stack, same collapsed (when >= 5):

        mach_msg_trap        985

I guess I'm off to Apple's website to see if I can find the relevant source and try to figure out why this is happening.