The Mac Pro (Jan 2008) has been the best computer I have ever used/owned. I bought it because I wanted a great tool for creation, in a variety of different mediums. It has not disappointed me in the least. It is a very capable machine, I am almost always multi-tasking, and it really does a great job using the eight different xeon cores available to it.
I have done 3D animation, graphic design, web design, video editing, music composition, and rendering. It has excelled in everyone of these areas. In fact I have done many of these things simultaneously. Rendering a 3D animation and video editing at the same time for example. It handles it no problem.
Mine came with the latest version of Mac OS X 10.5 Leopard, which also has boosted my ability to multi-task.
The truth is though, despite the fact that I do all these very intensive things. I am not sure I've needed as much power as the Mac Pro delivers. I think the new iMac would have been totally sufficient for my needs and a lot less expensive.
I am not sure you can do a dual monitor setup on the iMac like you can on the Mac Pro, which I absolutely love and recommend.
One of my favorite things about the Mac Pro is how well designed it was. Its attractive, its quiet, and easily expandable. A month ago I put in two additional hard drives in it, it only took a minute. It is very elegantly designed.
My Mac Pro set me back about $3,000 dollars. As soon as I ordered it, my heart kind of fluttered and wondered if it was worth it. Once I got it and used it, my worry melted away with delight. If you compare the prices with a similarly configured system from Dell, it will cost you about an additional $1,000 dollars.
I recommend buying more hard drives and memory from a different supplier than apple. They charge quite a bit more then what you can find else where.