I have these very same $2.95 fans in the system I am currently constructing.......They work just fine on 12v with fairly good flow and VERY quiet......
Though as others have discussed it would be nice to have the option of turning them up a notch......Many of you may be intrested in the details of the system they are going in and that and pics can be found here:
BlackMax
I also bought a 24v 6amp PS from the same vendor when I ordered the fans for $4.95 which I would love to be able to regulate from say 12 to 24v.......I am guessing a reostat would do the trick but am unsure of what exactly to get and where to get it.......
Guess I am STANK cheese here for a while lol