I'm very pro-Mac but my usual advice to most people is to look at what you want to do with the machine and then decide.
There are some specialist areas where PCs still command pretty much the whole software market and Mac representation is, at best, one of 'poor relations'. Accounts software springs to mind as one example. If it's mission-critical to you then you should consider this. Suggestions of Parallels or BootCamp are all well and good but both of these inflate the price as you have to purchase a copy of Windows - so you can wave goodbye to around GBP100 just for that. I also tend to think running Windows on a Mac does seem rather perverse - you'd be better off buying a cheap Windows box.
Generally, though, I've yet to meet a Mac user who does anything other than enthuse about their machine whereas all PC users tend to do is whinge about theirs.
Macs do generally last longer - my parents iMac lasted about 8 years before it was finally replaced with a Mac Mini a couple of years ago.
In terms of warranty I think AppleCare is pretty much essential for an iMac or laptop as if the screen fails this can be an expensive repair. If you purchase a laptop from John Lewis they do give 2 years warranty free of charge. You'll also get 4 BA miles per pound instead of 2 from the Apple Store (hey - this IS the BA board !).
As to the claim by KenJohn that most techies dislike Macs because they can't 'fiddle' this is not really true. I'm head of IT where I work and I much prefer Macs because they cause me far less hassle and they are far easier to fit into existing networks. The end users tend to like them as well so it's a win-win proposition. An XServe as a file server leaves a Windows box for dead both in terms of specification and value for money. I'm aware some IT 'professionals' look on Macs with disdain but it is usually ignorance and fear of the unknown when you get right down to it. They also want to protect their jobs by having systems that are hard to set up and administer.
I'm also not sure I 'buy' the argument about peripherals being more expensive. I can't think of anything to buy that isn't a generic item. Memory, USB and FireWire drives, screens, mouses, keyboards - you can buy a cheap one and just plug it in. But if you must go to PCWorld or Maplin then, really, you deserve to be ripped off...
BAH