How easy is it to buy upgrade/replacement parts for a Mac Pro?
Apple uses custom logic boards, but I've heard of people upgrading the CPU if it uses the same socket type. The power supply on my 2008 Mac Pro would be hard to get to for a replacement. The key upgrade options are new hard drives, more memory, and better video cards. I've used those three to keep my '08 Mac Pro running fast enough to more than meet all of my current needs.