I've become a little jaded, I guess. The hardware innovation is great, but it's the software that determines obsolescence. Given the way software is interconnected these days, and the necessity for constant security patches, I'd be surprised if OS updates for it continue for more than 4 years or so (Snow Leopard is 4 years old).
Even if you're just doing coding or running database stuff on it, eventually OS limitations will catch up with you.
I could certainly be wrong, though.
Apple usually prices mid-range versions of the MacPro around $2500 with top-of-the-range versions around $4000. That's a huge amount of money for a PC these days. Sure, apples and oranges, and so forth, compared to an Alienware gaming box or a traditional multi-CPU server. But it's still not an easy choice.
One advantage of the MacPro is that they hold their value pretty well, so if you don't hold on to them too long, you can get a substantial fraction of the money back for the next one. But if you wait too long, they're not that desirable - http://www.macofallt...-Desktops-s/2.htm
I've still got J's dual G5 in the corner - we stopped using it because FF couldn't be kept current. MoaT lists one for $199.
It'll be interesting to see how they position it. I expect it to be a premium box and that they don't really want to sell a lot of them. Bugatti doesn't want to sell millions of units. ;-)