Social Networks should be like email providers. You choose one that fits you best, or deploy your own, without having to worry not being able to communicate with others. Maybe we are long overdue for an open standard protocol for social interactions on the web. If you come to think of it, when the personal data itself isn't the property of the company behind the social network, there should be no reason not to share…
This is partially correct. Slow Social would be a lot better if all your friends joined. However, my accommodation for this is that any post can be sent as en email as well. This lets you loop in people that aren't part of the network, and maybe never will be. It's not a perfect solution, but I hope it's better than nothing.