Same issue as others have had. Though originally intended to be posted to this thread, somehow my post ended up on another related thread. See details here:
http://discussions.apple.com/message.jspa?messageID=10499969#10499969
Basically, issue occurred on
* 2006 MacBook Pro (2.0GHz Core Duo, 2GB RAM) running Mac OS X 10.6.1 "Snow Leopard"
* two (2) 2008 Xserves (Xeon quadcore systems, 6GB RAM) running Mac OS X Server 10.6.1 "Snow Leopard"
The issue did NOT occur on a 2.4GHz Core 2 Duo 20" iMac running Mac OS X 10.5.8 "Leopard". From small sample set, this indicated the issue may be restricted to "Snow Leopard" only.
In all cases SystemUIServer was consuming the CPU, with both cores on the MacBook Pro running full tilt, and on the Xerves at least one core spiking to 100%.
On the MacBook Pro, I also noticed the following entries appearing over and over again in the Console system log:
"Nov 1 01:04:53 MacBook-Pro-15 com.apple.launchd[1] (com.apple.newsyslog): Throttling respawn: Will start in 1 seconds
Nov 1 01:04:54: --- last message repeated 1958 times ---"
with the number of seconds varying from 1 to 10 seconds. I can't even begin to count the number of entries showing.
Restarting the MacBook Pro did not help. As soon as it was back up, SystemUIServer once again inhaled the CPU and the entries returned.
Eventually I gave up, powered down the MacBook Pro, went to the iMac, logged into this discussion forum, and searched and found this thread. I tried what was suggested in turning off the clock on the menu bar, and that did make the issue go away. Re-enabling the clock, however, brought the issue right back (note this was during the 1:-2:AM EDT timeframe, with the changeover occurring at the beginning of that hour cycle).
In the end, I simply disabled the menu bar clock on all systems and called it a night.
Today, I found the MacBook Pro behaving normally once again. The CPU spiked after initial login, but it subsided within a minute or two and even with the menu bar clock enabled, all is fine once again.
I hope Apple fixes this bug before the next time change, as it caused a bit of aggravation to say the least.
And to the forum moderators who censored my previous post to this thread earlier today, I say, "Seriously?"