Does OS X Mountain Support USB 3.0 ?

My WD 500GB (bus powered) USB3.0 HDD appears a second or two after I connect it. I'm having a little trouble with my Seagate 2TB (AC powered) USB2.0 (TimeMachine) HDD getting detected without connecting and disconnecting it several times.

I am having the same issue with two different Seagate 500GB HDDs; they connect on boot or plug in, show up on the desktop and then eject themselves. The power stays on but they are not visible.