I'm currently evaluating whether to use RightScale to manage a production environment in EC2. I intend to use Puppet for configuration management either way (the declarative approach seems far better than running scripts), am running a somewhat nonstandard stack (e.g. MongoDB), and am uncertain about how much value RightScale would add relative to Puppet + Amazon's auto-scaling + another hosted monitoring system. Those who use RightScale, what features do you find important? Is its auto-scaling support (including keeping single instances running) more powerful than Amazon's?