It's clearly designed to be podcast-only Digg clone with a very similar AJAX interface that encourages users to Zap podcasts rather than Digg them. ZapZap is divided into audio podcasts, video podcasts, and channels and also offers the ability to one-step subscribe to any podcast with iTunes or via plain old RSS.
There are almost 90,000 episodes online right now, but given that anyone can add a feed, I don't think that's indicative of a user base. It's only a matter of time, though. The interface is nice looking and there's a fair amount of content on ZapZap.
One of my rules is to sign up my podcast onto every directory that I find. Well, ZapZap, here I come!
