To be honest, I've seen both: `GET /user`, without an ID, implying a list of all users, versus `GET /users` (with `GET /user` then returning a 404. I think it boils down to convention - I'm used to doing development using [Backbone.js](http://documentcloud.github.io/backbone/#Sync) which would use the `GET /user[/id]` way.

Since we're creating our own API, I don't have a strong opinion in the matter. `GET /user[/id]` _feels_ cleaner to me, but that's just because it's the way I've done it in the past. Let me know if you want it changed.