Love it! You've got the 960 grid, how about some other common page template sizes that the UI can snap to, like iPhone, iPad. I'd also like to be able to go into that mode so I only see native (moqup style) controls as options..

I often want to bang out a layout so I know I've got UI / distribution of controls sorted and then know my general widths / positioning..

If the snapping as good, and I could export or easily grab the positioning / pixels that's something I'd pay a bit for..

Keep up the good work!!