Does the 2011 iMac have SATA 3 support?
It turns out that there is SATA 3 on board, it just wasn't enabled until 4 May 2011. The Other World Computing blog has the details:


  While iMac EFI Update 1.6 is described
  as including “fixes that improve
  performance and stability for
  Thunderbolt,” it would also seem that
  an unadvertised benefit is that it
  also unlocks the full 6Gb/s, SATA 3.0
  capabilities of two of the internal
  drive bays.
  
  Unfortunately, the optical bay remains
  at 3Gb/s.