Xeons and P4s do better in band-width heavy, 'dumb' applications, like rendering and video encoding. No suprises there.
One important thing to look at is how close the AMD chips have gotten, considering that many of these apps have P4-specific optomizations. Also there's this whole thing where the A64s do slightly better in office stuff, and gaming, though lesser there.
...and NOTHING feels faster than a dual-Opteron w/ SCSI RAID 🙂.