I wasn't totally skeptical - we did RAC on AWS in tests back in the day using a third node as an iSCSI target, but it was a) sketchy as hell, b) not at all redundant, c) not something I thought Palm would go for.
It might work on something like OEL with ZFSonLinux using zfs send/recv. Larger implementation might want to investigate drbd or something like OCFS2, GPFS, AFS or Lustre (none of which probably plays well with cloud environments). Maybe Gluster but with trepidation.
(It was an AWS consulting shop with banking / military chops, whom could sell ice to enterprise eskimos.)