And yet this is what FaceBook, Twitter, Google, Apple and many other web and OS corporations are encouraging people to do - build on top of their platform (be that FB apps, Twitter API, iOS/Android apps or web apps relying on a single-signon). They all want to own the platform which everyone builds and consumes on, and turn everyone else into sharecroppers.

With this particular service, it might be really great for connecting people to provide each other services, but as it also relies on Google+ (which, for example, people have been arbitrarily shut out of), and is provided by Google of Reader infame, is it worth an investment of time or resources? Perhaps as an adjunct to other services, but I'd be wary of depending on it in any meaningful way, as you say.

That may sound like common sense, but see the examples given above of platforms which try to push both consumers and developers into reliance on one tech company for essential parts of their online identity (professional and personal).