Maybe I'm wierd, but I'll stick with the PC.
Currently, the only advantage the X-Box has over the PC is with it's chipset (system board and on the video adapter), as can be readily seen in the graphics. It may also have a slight advantage in the design of the player's controller.
However, there are works in progress for the PC that will even dwarf the advantages of the X-Box chipset.
It seems that every damn company is trying to find some way to up the performance of a PC. They are either creating new memory designs, CPU designs, and bus transfer technology.
By the time I decide to upgrade my current PC (probably within this year), I will have the ability to choose hardware that outperform the X-Box. In order for the X-Box to be a contender, it will always need to be redevoloped just like the PC. However, I can do very little more than play games on the X-Box, whereas I can do a bunch more things with a PC.
I couldn't see myself always having to upgrade my "gaming" system. However, I can see the advantages of upgrading my PC.