I know this isn't going to concern you TOO much, but I thought I'll add my comment anyway.

I'm on a Fedora X86_64 box running Firefox 3.0.11 (with no flash, but I don't think your site needs it anyway), and whenever I click the "Add a Widget" button, I get an error.

I provided the browser/OS details to help narrow the problem.

The screenshots make it look like it'll be a great app. Congrats on getting it out there.