Ok if you want to play the biased game, I'll have to do the balanced reporting for you. For this example we shall use current available purchases from the Apple store in the UK, and the Dell store in the UK.
The Dell Studio slim is a fancy looking PC with one of Dell's best price to component quality ratios. With a quad core 2.33Ghz CPU, 3Gb RAM and a 20" display you're looking at £598.
Apple's offering is difficult to find an equivalent. The Mac Mini is similar in style, and starts at £599. However, it comes with a 2.0GHz Intel Core 2 Duo, and NO display. It seems this is supposed to be a media PC, and they only give the option to ship it with a 24" cinema display, for £650 extra (which is ridiculous).
So, the mini is a pretty bad idea. How about the iMac. Well they start at £949, with a 20" display, 2.66Ghz Core duo processor and 3Gb RAM, which is pretty comparable I'd say. Er, so it's not so much that the PC is cheaper at the low end. It's that this cheap low end PC from Dell gives the same components as the Apple equivalent for £350 more.
I'm sorry to say, but from a cold hardware point of view, you'd have to be stupid to buy a Mac.
Yes I realise Dell's all-in-one offering is overpriced. I don't care, Apple doesn't offer any cheap alternative to its all-in-one. Dell does.