I thought long and hard about this and it really didn't come down to a hardware decision at all. I'd buy a computer that ran on hamsters in wheels if it was easy to use and had all the capabilities I need.
The specs for the latest Toshiba Qosmio dual core machines are very simliar to the MacBook Pro: same CPU, same graphics cards etc., yet they're a few hundred quid cheaper. But with Macs, you get what you pay for: design, simplictiy and well intergrated components. However, I personally think the MacBook Pro is over priced, I don't really like the look of it and the keyboard is too small. It could have been made much bigger if they'd repositioned the speakers and reduced the size of the touch pad.
I've upgraded from a 2.33GHz P4 Sony Vaio notebook (which I'll still use) to the 17" iMac 1.8GHz Core Duo. The iMac is truly great. I don't think any PC would have given me the same feeling of money well spent. I'm converted. Not specifically to Macs, but OS X.
I can get all the apps I need on OS X, plus loads of free downloadable stuff - just like you can on Windows XP (although sometimes the open source stuff is hard to install).
You never know Microsoft could surprise us all in January with Windows Vista - a stable well designed Operating System... but i doubt it. If Steve Jobs had any sense he'd make next version of OS X run on PC's and release it in October 2006.
However, the thing that makes Windows so unreliable is the vast amount of hardware it has to support. OS X is designed for Macs with specific components, but under the cover Macs are looking more and more like PC's.
Still, I reckon the iMac is probably the best computer for its price at the moment.