As difficult a time as EBS is having, it's good to see some other alternatives pop up. This will definitely put the pressure on the EBS team to clean up, if they weren't already under immense pressure to do so.

A word of caution, though: Rackspace is just getting into this ballgame of on-demand virtual block devices. There will probably be gaffes (though, hopefully not as bad as EBS of late), so, as per the virtualization commandments, build expecting failure.

Edit: Also, Rackspace had perfect timing for this announcement, the day after catastrophic EBS failure. Coincidence, or astute choice in launch dates? :)