I started out with the 2.66GHz 4 core (1st gen) back in 06 then I sold it off a year later, just hung around with a 15" mbp.
Then early last year I had the 2.8GHz 8 core mac pro, loaded it up with 16GB of RAM, sold it off mid last year, hung around with a 17" mbp.
And I ended up selling the 17" mbp for the 15" unibody mbp and used it until I got this mac mini and sold it off. And right now I'm chugging along fine with the mac mini + 24" LED ACD.
Basically since 06 I've been through all the 15" mbp models, 17" mbp and hi res models, 20" ACD, 23" ACD, 30" ACD, 2.66GHz mac pro, 2.8GHz 8 core mac pro (actually I had it twice rigged it up and sold it good prices on eBay). I actually got tired of the Mac Pros since most of the time the mbp did the job ok enough but of course I wanted more power later on.
But the new Nehalem intrigues me. I'm currently just waiting until the 3.2GHz nehalems are officially announced (originally I was going to pick one up either the 2.26GHz or the 2.66GHz model at my local store) but I'm going to wait until around summer.
Actually I'm going to wait until SL is shipped along with the Nehalem Mac Pros. I have a very strong feeling it'll be worth the surprise (speed bump, much faster with SL as it is right now with Leopard, etc..).
I dont use the Mac Pro's power 24/7 but I do really really heavy multitasking things with 6-8 spaces open and the mini so far restricts me down to just 4 spaces. Once or twice a week I might render something hd movies but while the mbp takes 2x longer, I have some time to kill, might as well save money. But I noticed recently my hunger for power grows again.