I just put together a near identical (specced) PC on scan, and it come up to roughly the same price as the i7 27" iMac, so I can definitely understand the appeal of the iMac for professional use, and the pricing seems to be more than fair. I can't really see the use of a 27" screen for everyday home use outside of enthusiast gaming (which would require the insane GPU power of a PC), but it seems to be an impressive deal all the same.
For mid-range laptops and computers, PC's seem to be winning on value everywhere I look. I'm going to be buying a new laptop within the next couple of months, so if Macs manage to become more competitive price wise in that timeframe, then I might look into getting myself one, especially if steam does go ahead with porting the source engine to macs. I have a decently powerful desktop PC for gaming, it also dual boots into Ubuntu for work stuff).
I can't really comment on applications any further without educating myself a bit more, but I can't imagine I'm wrong in saying anything the Mac has, Windows also has and visa versa. Out of interest, how easy (or possible) is it to set up a OSX/Windows/Linux setup on a MacBook?