The Streaming API delivers HTTP push technology (webinar signup). Check out Pat's description of the Streaming API, where he gives one great use case – polling, describing the Streaming API as "a more elegant, efficient, scalable alternative".
This is a smörgåsbord of new technology. Apex REST will let you write killer integrations, easily. Chatter REST will let you take Chatter to mobile devices and other apps in a much more intuitive fashion. And Streaming API will bring push technology to your apps.
Next steps – sign up for the webinars (see the webinar signup links above). It's okay to sign up for all three 🙂
Note that these APIs are all entering developer preview. They're not for production – and of course they may change. Details of the developer previews will be made available during the webinars.