As per the discussion on IRC May 17, 2011.
Add the ability for clusters to be stopped and started later while preserving data. AWS instances with an ebs root drive can be stopped and started again later while preserving data.
Ideally, the Start/Stop ability will be available to other services besides Amazon.
A note for amazon ebs instances (and possibly other services): when each node is started up again, it will receive a new IP address. Thus, the configuration files on each node may need to be changed to reflect the new IP addresses.