I dug around to see if we could get this in JSON. Here's the [docs I found](http://wiki.openstreetmap.org/wiki/API_v0.6#Details_of_a_user), which seem to say that no, we can't. If you search for 'json' on that page you'll see that one or two other endpoints support json via a file extension in the URL path, but [testing](http://master.apis.dev.openstreetmap.org/api/0.6/user/1000.json) indicates that json is not supported for the user details endpoint.