For REST, I mainly use the plural form to indicate the path to the resource. But you should also take Cacheablility, the frequency of changes and the turbidity of the resource. In my case, resource collections mostly deal, so I used a plural form.
The reason for this is because, for example:
http:
will serve the URI to GET a johndoe user belonging to your user collection.
http:
will be used as a URI for GET for all users and can be easily used in the request URL:
http://www.example.com/users?limit=5
- URL-, POST :
http:
Oreilly RESTful Web Services Cookbook