Just for kicks I did a component price comparison:
$209.00 Intel Core i5 2400*
$105.00 Western Digital Caviar Black 1TB WD1002FAEX
$29.00 Microsoft Comfort Mouse 4500 Grey
$49.00 Microsoft Sidewinder X4 Keyboard
$69.00 Antec New Solution VSK-2000 Case
$499.00 ASUS VE278Q 27 ASUS VE278Q 27" Widescreen LED Monitor
$139.00 HIS ATI Radeon HD5770 1GB
$149.00 Pioneer BDR-206 Blu-Ray Disc Writer OEM
$69.00 Antec Basiq 500W Plus Power Supply
$105.00 Microsoft Windows 7 Home Premium 64bit with SP1 OEM
$69.00 ASRock H61M-VS Motherboard B3
$58.00 Kingston ValueRAM KVR1333D3N9/2G 2GB DDR3
Total: $1549.00
27-inch iMac
2.93GHz Quad-Core Intel Core i7
4GB 1333MHz DDR3 SDRAM - 2x2GB
1TB Serial ATA Drive
8x double-layer SuperDrive
ATI Radeon HD 5750 1GB GDDR5 SDRAM
Apple Wireless Keyboard (English) & User's Guide
Magic Mouse
Country Kit
Total: $2199.00
* Tried to match the iMac's CPU as best I could but I'd say the new socket 1155 i5 would kick the iMac's arse. My favourite supplier no longer stocks 1156 CPU