It’s not at all clear what the root cause of the problem is, but we’ve noticed a big uptick in people complaining about performance issues on new 27-inch iMacs on Apple’s support boards.
The most common symptom seems to be incredibly slow Flash video playback, others complain there’s a bug forcing the hard drive to spin down. There’s even reports these Macs ship with a corrupted Snow Leopard build installed on the computer.
“I just upgraded my 24" iMac to the new 27" iMacs that just came out. Well, now every flash-based site like youtube or hulu runs unbelievably slow. Looking at activity monitor, Flash is hitting about 100-110% of my cpu. It basically makes the browser unresponsive and the video is choppy,” one user claims on the Apple forums.
It must be stressed these reports do not claim all new 27-inch iMacs are so affected, it seems to be a problem (or series of problems) which afflict only some units at this time.
Topic : New 27" iMac — Slow Flash Video