I'm seeing the same problem. It's happened 3-4 times this week. Only when I'm at home and off the work network. The whole UI gets bogged down and I can't type anywhere. If I'm persistent, I seem to be able to change apps by clicking on whatever is visible, but I can't do anything with them.
Here's a few relevant entries in my windowserver.log:
Oct 16 22:29:16 [60] kCGErrorFailure: CGXDisableUpdate: UI updates were forcibly disabled by application "iTunes" for over 1 second. Server has re-enabled them.
Oct 16 22:29:17 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:17 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:18 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:18 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:19 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:19 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:20 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:21 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:22 [60] kCGErrorFailure: CGXDisableUpdate: UI updates were forcibly disabled by application "iTunes" for over 1 second. Server has re-enabled them.
Oct 16 22:29:22 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Oct 16 22:29:30 [60] kCGErrorFailure: CGXDisableUpdate: UI updates were forcibly disabled by application "Microsoft Entourage" for over 1 second. Server has re-enabled them.
Oct 16 22:29:31 [60] [cps/setfront] Failed setting the front application to Activity Monitor, psn 0x0-0x2da2da, securitySessionID=0x315a74, err=-13066
Any ideas?