"Quiet and very fast, but expensive"4.5 starson by longofest
Pros: Very, very fast and quieter than you'd expect. Nice port/expandability options (see caviat in cons)
Cons: older PCI cards won't work in PCI-e slots, expensive
Summary: I have had my brand new Quad for about a month now as an upgrade to my aging Dual 1Ghz Quicksilver 2002 machine that has served me well over the years.
Setup was very easy. The migration assistant worked as advertised (placing old computer into target disk mode and transfering old info from it to new computer took 45 minutes), and I was up and running in under an hour (not bad for as much crap as I have).
I was a little disappointed that I could not move some of my expansion cards over to the new PowerMac because the new Mac uses the advanced PCI Express slots for all of its expansion, which is not backwards compatible with PCI cards despite the name. However, I knew this going in, so its not too bad. Number of ports and expandability is great. I really like the inclusion of 2 Gb Ethernet ports on this revision, which allows me to sync my PowerBook with one cable, and connect to the net with another.
Performance is great. I used an application that I had written to compare one CPU from my Dual 1Ghz to 1 CPU from the Quad, and the Quad is about 4x faster (this is just one CPU). The app was Alti-vec heavy, so keep that in mind. A less alti-vec heavy app saw a less dramatic speed improvement (more like 2.5x faster, which is more like the clock-speed differential).
While my app was not multi-threaded and was able to reside completely in each processor's Cache (so it is only useful in comparing the processors themselves), I can say that general tasks also feel much snappier as well.
Final notes: the liquid-cooling of the Quad does wonders to keep its noise down way low. It is less than half as loud as my G4, and is quieter than my PC as well. Nice job Apple.
I recommend this if you have multi-threaded Apps that can use all 4 processors to their fullest. The machine has been good to me so far, and I believe it will be good to you as well. Of course, get Applecare as well. You never know...