I know what you mean hen you talk about the "1/2 of what the iMac would cost", have been a PC-guy for years. But since last year, I got really interested in Macs and now I do understand why people are willing to pay twice as much. I'm one of them! (waiting for the new iMac as well, to be my first!).
1. (Especially the iMac) isn't much more expensive then a PC. Not when you count the all-in-one concept (look at all-in-one PC's, they can't match the iMac in speed, and costs almost as much as an iMac!), the 21" or 27" IPS LED display (seen any IPS LED displays cheap lately??), the power (i7, as much RAM as you want/need, up to 2TB HDD),...
2. The operating system OS X, which you can't have with pc's (hackintosh only works on specific configurations and needs a lot of tweaking, doesn't represent the real OS X experience as it should be). PC's are Windows-only, but Macs combine OS X and Windows in one!
3. The design: Not something everyone would care about, but as an architect/photographer/designer/perfectionist

... it does care. And when you have it once, you don't want those cheaply built PC's anymore.
Shure there are disadvantages: You would pay more then you would do when buying a PC (however it wouldn't match Macs on every aspect) and you are limited with the hardware (especially the GPU might be a let-down. If you are a pro-gamer, you wouldn't need OS X or a Mac anyway).
For me the decision is simple: Buy a Mac, unless you are a pro-gamer or don't give a **** about all those design-blabla-OSX-blabla-display-blabla-..., and just want a computer which contains
that CPU and
'so much' RAM