Out of curiosity, could you show us the components that you would put together to create a PC that is at least as well equipped as the iMac, keeping in mind all the things mentioned here? Since you make it sound so easy, it shouldn't take you too long to put it together here.
You had better be more specific. I've seen a few times people try to make such a comparison, and then someone else inevitably points out "oh but it doesn't have Thunderbolt", or some other niche or picky thing, and say it's not a fair comparison. So, define the important specifications, or you'll end up shooting for several different sets of goal posts, and/or moving them.
Besides, doesn't Tonymac have a whole lot of Mac-compatible parts and combinations listed already? If you're actually interested, surely you'll get a whole lot more info there than jav could reasonably list here...
If I had the know-how, I'd definitely build my own PC next time, and use my iMac as a monitor. Alas, PC-building is not an area of expertise of mine.
Cheers.