When I got my Mac Pro, I was a little disappointed at its overall performance. I mean, it was a beast (a total monster) when it came to processor intensive tasks, but the system felt, during casual use, sluggish. App loading times were longer than the dual core iMacs at my school, and my buddies $1,000 Dell with Vista felt a bit more robust with casual use. I finally narrowed it down to that POS stock 500GB Seagate HD. It was one of the nosiest drives I had ever used, and it was insanely slow. I was scoring in the low 40s on the xbench drive test, a little lower than my USB 4200RPM HD (years old, too). It sounded like tacks falling on glass whenever I opened iTunes. I finally upgraded to the new WD 640GB drive, and re-installed OS X and all my apps on it. It feels like a totally different computer. When I open an app, there is no delay, no noise -- it just opens. I am scoring in the high 90s, low 100s with the new HD. I also added another 2 gigs of ram, and although the difference is not nearly as noticeable, multitasking is much, much nicer. I am just shocked Apple put such a slow hard drive in such a nice computer. I am not sure what the deal is with the 7200.10s in the Mac Pros (They do better in other computers), but it was almost unusable. If you have a stock Seagate drive and are unhappy, definitely consider upgrading; it is well worth it.