I love my Mac Pro, and have dumped a lot of money into it. It's excellent and stable, yet I'm afraid to use Lion and still don't like Final Cut X. You really have to focus on what tools you want to use, then build the system that works best with those (software) tools.
The next FCPX update looks really great. But to each their own.
Lion is a problem. I've noticed a few things in Mountain Lion that may correct some of that.