This is also the most exciting feature to me. But, looking through the reviews, it sounds like the buggiest feature. Worst of all, they process your UIs server-side and then send the code to you. Unacceptable.

I just picked up Dapp (http://dapp.kerofrog.com.au/) and put together the first screen of an app that's been bouncing around in my head for a couple weeks. It was pretty intuitive and quick to put it together. I also confirmed that Dapp generates all its code client-side, by using the app only in Airplane mode. Looking over the code, I'm not thrilled about the coding style, but it's not bad for auto-generated code.

So I can't speak for Interfaces (I wasn't going to drop $10 on an app that had terrible reviews about the one killer feature I need) but it seems like Dapp is a winner. YMMV.