What kills Google+'s utility and might kill Facebook's stream is the lack of a way to keep track of my high-water mark of what I read through the stream, and always feeling the perception that the software is keeping things from me.

Whereas with Twitter, if I don't want to read something, I unfollow, but its fairly easy for me to track what I've read and know I'm reading all that I possibly can and want to.

Facebook adding subscriptions is interesting, now lets get a good desktop client and high-water-mark syncing between web, phone and desktop.