This looks good. But I do have some doubts regarding its querying abilities. As far as I can tell, you can only define a range of data to be fetched (limit). If I want to query for a particular value, i.e. fetch all users matching name - that doesn't seem possible. Or am I missing something?
Well I personally find JSON easier to read and write than XML. Though it might be different for some people, I don't know. It would differentiate the whole thing a bit more from the usual XML approach by interface builder.