Ingenious. Check out the Rocker by Studio Oooms of the Netherlands (that's 3 o's).
But sometimes we wish we could design our own...You don't like the spare back of this one? That's okay. Then how about this one?
(see below the jump)
Still too austere? It's okay! The Oooms Rocker is neither of these.
The Rocker actually consists only of the plywood and steel runners attached to the chairs pictured. Oooms designed the runners to attach to almost any four-legged chair and turn it into your very own customized rocker. Best of all, you can change it back into a chair when the time comes. We immediately started fantasizing about our perfect chair-turned-rocker combinations.
You can find U.S. and online retailers here.