My first computer was a MacIntosh Classic. A stunning piece of machinery and anyone that remembers better can correct me, but I think 2 Mb or Ram and 40 Mb hard drive. Ah, the glory days. Still like Macs, just not much point for the same reasons as Scott.
I'm kind of in the same boat as Matt, but not in any hurry to get a new one. Running a P II 333, 384 Mb Ram, 64 Mb Vid card, so all is still pretty good, at least for what I use it for. Waiting for DVD burners to come down in price a bit more, and get the spin rate up.
By the time I get a new one (late fall maybe), I'm hoping for 3+ GHz, 512 Mb Ram, 60+ GHz hard drive, 128 Mb Vid card, (probably pull my soundblaster Audigy out of this one and put the old one back in), CD-RW and DVD RW, Zip and away she goes. But the price for that needs to come down quite a bit. What is it, 3 months for processor turnover in terms of price? 6 months should make that all quite affordable. Monitors should be good by then too.
My wife (the boss) has a Dell laptop she loves, so probably another Dell. It all depends on price for the same quality of components.