OpsWorks gives you better features, try out to start a small stack and then also have a look at the default cookbooks, there you can see what you can do with OpsWorks: https://github.com/aws/opsworks-cookbooks
I have a webapp that I built, that utilizes rackspace's API and chef. I have a chef server that I use for all my configuration management, I have a Rails app that I use to talk to my chef server to manipulate machines, or rackspace's api to spin up machines, and I am building "triggering" into it (low disk space, high CPU do X). I am able to change IP addresses, spin up a machine with a specific stack etc. Granted this isnt the default chef-server, but the ability to do all this stuff, and not be locked into AWS is there.
