I just installed mine in the last hour, and man, what a difference!
Before, I'd hear the variable-speed fan almost constantly, but the most annoying part was the constant 'whine' of the power supply fans. After the replacement was installed, the machine is as quiet as any recent tower I've experienced, and I've yet to hear the variable-speed fan at all!
This machine is an original MDD dual gig, running 10.2.4, and I *did* apply the firmware update that was supposed to provide some improvement (which it didn't). I'd say it now sounds about the same as our other desktop: a Sawtooth G4/400.
I'm happy as a camper can be... And I have no plans to sell the old PS on ebay. I think I'll hang on to it as a backup, unless someone else comes along needing it.
John-o