It was leaked a long time ago and its existence was leaked even before that, but Dashcode is now officially available in beta from Apple. You have to have an ADC account (free membership is fine) to get it. It's on the ADC site under downloads. I just downloaded it. I've been wanting to create a widget to go with the app I'm developing. That'll give me a project to work on in order to learn how to use Dashcode.