I'm one of the co-authors of the OStatus spec and the lead developer on StatusNet (http://status.net/) and the ActivityPump (http://activitypump.org/).

I think the secret weapon in the OStatus arsenal is that there are literally hundreds of millions (literally HUNDREDS OF MILLIONS) of PubSubHubbub-enabled feeds on the Web.

Blogger, YouTube, WordPress.com, Tumblr, and Posterous as well as StatusNet and Diaspora* all provide PuSH-enabled feeds. That's a huge body of content to follow in real time.

Another good part is that PubSubHubbub will help with SEO -- Google Search bots subscribe to PuSH-enabled streams, which gets you indexed faster. Lots of incentive is good for getting things done.

There is distinctly lower support for the other parts of the OStatus stack. But I hope we'll see this stack continue to develop.