I agree that the service is still in it's infancy and I think that it is worth pointing out the beauty of this fact. Rather than jamming a bunch of features into a release, they seem to be staggering their features well enough to launch features that actually work.
I see companies launching with as many features as possible in their app all the time. Simple seems to be following a process more akin to the Lean Methodology ( The Lean Startup | Methodology ) where the minimum viable product is launched and then iterated upon.
Their software definitely seems much less buggy than most (IMO).