Although Apple is moving away from IBM's PowerPC CPUs for desktop and laptops in the future, IBM is still sitting pretty on the most recent Top 500 list (Just 2005) of the fastest supercomputers. An explosion in clustered computing leaves IBM in the 1,2,5,6,8, and 9th positions on the map, with their number 1 BlueGene/65536 clocking in at a whopping 136,800 GFlops (to put this in perspective, Earth Simulator, the number one 6 months ago, is a paltry 35,860). System X, the top Apple cluster on the list, comes in at 14 with 12,250 GFlops. Further, 16 of the top 25 are PowerPC based (and only 1 of them is a Mac cluster).
There are, by the way, 4 XServe systems on the list, coming in at 14 (System X, Virginia Tech), 66 (Turing, UIUC-CS), 162 (Dawson, UCLA), and 166 (Xseed, Bowie State University).