I think it might have to do with your home internet speed. I had forgotten my ipod when I went to work today, so I decided to use Zumocast. I already had it all set up, so I thought 'what the hell, I'll run it'.
I had so much buffering that the app was barely usable. I threw on Pandora and had perfect streaming with no buffering. That leaves 2 options, either the app is crap or the home internet connection is the issue. And since people are posting that they're not buffering, that means it's probably the home internet and not the app.