Mid-2011 iMac running Lion slows down after a few hours.

Yes, I know that PPC APPS can't run; I was wondering if remnants of PPC code might be a factor. Again, according to Activity Monitor the 2 items using the most CPU percentage during the slow down are #1, "activitymonitord", and #2, "SystemUIServer".

OK.

Yes, "All" is selected; Activitymonitord was about 37%, and SystemUIServer was about 33%. I restarted the iMac and they both dropped to 2.1% and 0.4%, respectively.

Here is another data point: if I put the iMac to sleep, then it doesn't slow down (which is the way it is supposed to be); if I use the iMac for a few hours, then it starts getting slow and the CPU percentage for SystemUIServer and Activitymonitord go up.

Haven't had time yet; will work on this. I'm also going to take a sample of the SystemUIServer process the next time I experience a slow down.

OK. I've had time to go over these. The vast majority was stuff I already pretty much knew. However, I didn't see anything that really addressed my situation. If I knew what the SystemUIServer process accesses, I might have a better clue. All I know for sure is that a restart fixes things for several hours.

No

I think I may have found it. I've used iStat Menus for years, but while it didn't cause a problem on PPC machines, there have been reports that Intel machines have a bug in them that causes iStat to hold on to memory and CPU cycles, causing a major slowdown. I uninstalled iStat last night then shut down my iMac. I fired it up at 7:00 A.M. this morning and 9 hours have gone by without a slowdown. I'll leave the iMac running overnight and see what happens after 24 hours.

Hey, it was YOUR suggestion to Google "SystemUIServer"; it brought up several posts that described my problem and pointed to iStat Menus. Like I said, I never had a problem with them on PPC Macs; those reporting problems seemed to all have Intel Macs. I've always hated Intel systems, but I couldn't hold out until Apple releases their non-Intel iMac, so I have to put up with this one. I wonder if the problem would exist if Apple used AMD chips instead of Intel?

Anyway, removing that app fixed a large amount of the problem but I still get a slowdown after several hours; just not as bad. Unless I launch System Preferences, that is, where it still takes about 2 minutes to launch after the iMac has been running for several hours. Without the slowdown, System Preferences launches in 2 SECONDS.