There are only 2 types of bearing coming in fans
1: Fluid Bearing (cheaper cost, less life)
2: Ball Bearings (higher cost, longer life)
some fan manufacturers as well include a combination of Fluid and a Ball Bearing, which are done in most of the fans. even with fluid bearings, the MTBF is 3 years, after that the fan starts giving out noise (happens in many OEM CPU fans). but you will notice one thing, fans with Fluid bearings are easy to rotate, therefore, ideal for noise reduction. its always recommended to get a BIGGER fan, as they tend to rotate slowly and draws out equal amount of air. a 1250RPM of 120MM bracket size fan is sufficient to draw out warm air out of the system quiet efficiently. but make sure, you equalise the air in = air out. does means, you have 2 80mm fans running each drawing in 30CFM and 1 bigger fan alone drawing out 37CFM. 5CFM +/- is still good ratio. in most cases, just one fan will do the job at back, as then it will draw in air from places (holes) making ambient cooling effect through out system (cooling motherboard, PCI cards, hard drives).
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"