Fellow Apple enthusiasts, I seem to be the first one to report this. I've found the cause of the infamous Mac "slowdown." I haven't seen this information posted anywhere yet, and hope to introduce a PROVEN solution to alleviate some frustrations with many Mac users out there. Don't return your iMac! Your hardware is fine. It is an Apple software issue that should be easily remedied with an update. I'm posting this here in the iMac section first, because many seem to believe that only the iMac is affected. This is false. It will probably affect any Snow Leopard machine. THE PROBLEM: Resource leakage, system slowdown, and slow/choppy Flash video playback while pegging CPU utilization for Flash Player, as observed in the Activity Monitor. THE CAUSE: MAGIC MOUSE drivers. Yes, the Wireless Mouse update is the cause. With the update installed, the problem will occur as long as the mouse is paired with the Mac. It will occur REGARDLESS if: - The Magic Mouse is in standby mode - The mouse is switched off via power switch underneath - The mouse is disconnected under the Bluetooth drop down menu at top of screen The reason I'm reporting the Wireless Mouse Update as the culprit is: I have a 13" unibody MacBook Pro (Early 2009) and purchased a Magic Mouse online. Received it yesterday - Monday, November 2nd, and updated the Wireless Mouse driver files via Software Update under the Apple menu. After the update, I noticed the same Flash Player problems mentioned online, and indeed, System Monitor showed about 104% utilization. Flash videos appeared to be running with 1/2 to 1/3 frame rates. *** THE SOLUTION: Remove your Magic Mouse using the Bluetooth Utility. - Click on the Bluetooth icon at top of screen, and choose "Open Bluetooth Preferences." Or, use equivalent steps via System Prefs. - Highlight the Magic Mouse, and then click on the "-" minus at the bottom of the window. - Your Magic Mouse will no longer function with your Mac, obviously. Use a different mouse to avoid the problems you've experienced. - The Flash video problem will no longer occur, and suspect the resource leakage may cease as well. A restart may or may not be necessary, but upon restarting my MBP, Flash video playback returned to normal, with about 40% utilization while streaming a single Flash video. The steps above are simply what I used to rectify the problem. I don't know if other bluetooth mice will cause this problem. I have not tested any other wired or wireless mice either. I'm just an average user who experienced and recognized the Flash video playback issue on my system. Upon seeing the problem occur, I simply reversed the last change I made to my computer, and found that this solved the problem. Both the problem and the fix are repeatable. The information here has been reported to Apple. DON'T RETURN YOUR COMPUTERS! I'm confident that once Apple is aware, a software fix will be made. Again, this will probably occur on any machine running Snow Leopard, and may be even more widespread. I will continue conversation with Apple on this subject. Good luck to us all in resolving this issue as quickly and easily as possible.