Power supply is warm

just bought a new gaming pc. I bought the parts from newegg and assembled is myself. i just shut it down after installing all of the drivers when I noticed the top of the case was warm. I opened the case and felt the PSU and it was warm.

anybody know why its a little hot?
her is my rig.

MB:
ASUS M4A785-M AM3/AM2+/AM2 AMD 785G HDMI Micro ATX AMD Motherboard - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$74.99
free Shipping

CPU:
AMD Phenom II X4 940 Black Edition Deneb 3.0GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM2+ 125W Quad-Core
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$155.99
Free Shipping

PSU:
OCZ StealthXStream OCZ600SXS 600W ATX12V / EPS12V SLI Ready Active PFC Power Supply - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$69.99

HDD:
Western Digital Caviar Black WD7501AALS 750GB 7200 RPM 32MB Cache SATA 3.0Gb/s 3.5" Hard Drive -Bare Drive
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$79.99
Free Shipping

CASE:
COOLER MASTER Centurion 534 RC-534-KKN2-GP Black Aluminum & Mesh bezel / SECC Chassis ATX Mid Tower
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$73.98

VIDEO:
EVGA 512-P3-N871-AR GeForce 9800 GTX 512MB 256-bit DDR3 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$134.99
Free Shipping

CD/DVD:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
HP Black 24X DVD+R 8X DVD+RW 12X DVD+R DL 24X DVD-R 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM SATA 24X Multiformat DVD Burner LightScribe Support - Retail
$30.99