I'm using my PowerBook G4 Titanium as my main machine for a while -- hopefully not long, because this is insanely slow. I'm trying to understand how it was wonderful five years ago, and now painfully slow, when I'm just running a browser and iTunes and gmail notifier and not even a terminal. I figured it out: the I/O is making it seem hellaciously slow. I used to have a FireWire iPod; now I'm using a USB iPod (thank you, Marshall). I used to be satisfied with my built-in 30 gig hard disk; now I'm using an external half-terabyte disk. Here's the kicker: this machine doesn't support USB 2! It was built back when firewire seemed like it was going to win. Firewire lost, though, at least for commodity consumer peripherals, and I'm hamstrung by slow IO.
I'm picking out my next mac, and I'm having a hell of a time deciding between almost all the form factors. I need one now, can't wait until after Macworld, so buying a monster macbook pro seems like a bad idea; I'll just be kicking myself when the prices drop and a new mindblower comes out in two weeks. The iMacs have the combination of tons more computing power and disk space for less money, but I've already got a huge wonderful display. (Hmm, could I use an iMac with the built-in display and my widescreen external display? Mmm, tasty!) And of course, I adore the idea of a Mac Pro, but I got one of those a few years ago and immediately discovered I would rather have a laptop. The one that I can totally rule out is the mini; 2GB ram just isn't how I roll. Probably the thing to do is to get a Mac Pro now, and plan on getting the rumored new subnotebook as my next planned purchase. Buying components instead of all-in-one's is the most flexible, but least portable, solution.