The Apex REST API documentation states that
Apex REST is currently available through a pilot program. For information on enabling Apex REST for your organization, contact salesforce.com.
However, I can't find this wording or reference to this "pilot program" anywhere else, or dates on any of this information, including a technical library post on using the Apex REST API.
Is the API still in
pilot mode? If not, what Editions of Salesforce is the API enabled for?