With the Poke app, you can poke or send a message, photo, or video to Facebook friends to share what you're up to in a lightweight way. You can poke an individual friend or several at once. Each message expires after a specific time you've set, either 1, 3, 5 or 10 seconds. When time runs out, the message disappears from the app.
This seems like it will eventually be a new revenue stream for the 'book. I can see them presenting an ad of some type (probably video) before getting to see the "message, photo, or video." And as usual more people will go along with it — while complaining about it — than quit over it, so it will be successful.