(1) I don't see how one Tent entity contacts another proactively - it looks like A can't message B unless B has already chosen to follow A. If this is so, is it an anti-spam measure? Given that StatusNet etc. are infested with spam, it seems like a very wise one :-) On the other hand, it is rather limiting as compared to centralized platforms, don't you think?
(2) I don't see how you maintain the promise of a portable identity when your identities are hosted URIs. Eg, if my identity is tent.is/foobar, and I want to move to a different host, how do I do that? I can download my data, sure. It looks like I can even bounce from tent.is to another data server. But unless I want to break all my social connections, don't I remain at the mercy of tent.is? This strikes me as a rather unsolvable problem, but it would be reassuring to clarify that you're not solving it :-)