So I guess I originally though that the `successCb` could get called multiple times as we evaluate more contacts asynchronously.  If I understand correctly, though, we hold off calling the callback at until we have the full results, right?

I was just wondering if it should be more cursor-like with `successCb` called multiple times with the final call passing `null` to indicate completion.

I guess I get the sense we might evolve this API a bit as the export code starts using it, etc.