Consider price and expandability as elements in your decision too. A desktop PC can be built to any spec you like, and can easily have extra bits retro-fitted to it via PCI cards. Beyond a few simple things like memory upgrades, this simply isn't possible on a Mac.

The upside of this is system stability - most PC crashes are due to dodgy drivers. The downside of course is that some of the more unusual add-on extras (multi-channel sound recording cards, for example) won't work with Macs, so it restricts your choice of hardware (sometimes to zero).

Also software availability. Macs famously have some of the best graphics manipulation and desktop publishing software. But more everyday software isn't necessarily available for Macs - the proliferation of downloads for Windows software doesn't always have Mac equivalents.

Graham.