Rackspace is open-sourcing the specs for its Cloud Servers and Cloud Files APIs under the Creative Commons 3.0 Attribution license, enabling third-party developers to copy, implement and rehash them as they see fit.
In addition, The Rackspace Cloud (formerly known as Mosso) has made available Cloud Files language bindings along with technical guidelines for Java, PHP, Python, C# and Ruby under the MIT license through GitHub. Rackspace aims to offer a reference implementation in Python soon and in a press release casually mentions it “is aware of Ruby, Perl, Java, and Twisted Python Cloud Servers bindings”, which are all in the process of being developed.
However, I don't think it's enough to offer up an API. When I think about how successful NFS became, it's clear to me that it was the combination of offering up the API as well as a reference implementation and test suite. The NFS team also sponsored "Connectathon" events where everyone could check the interoperability of their ports.
I know that the two domains are not the same. I know that the NFS implementation was not "open source", but rather commercially licensed (there really was no equivalent open source concept like the Creative Commons in the 1980's).
The point I'm making is that if Rackspace wants this to truly become the industry standard, they need to actively foster the community. Even to the point of enabling their direct competitors with a reference implementation of their server side abilities. Rackspace should be confident enough in their lead and implementation to do so.