A few comments on Scratch:
I'd really like to be able to browse the code for the projects on the web site. (Unless there's some way I missed.) You can download the projects and presumably see the code that way but that's a bunch more steps and not very good for exploring. Since there isn't much documentation, it would be helpful to quickly look at other people's code. It doesn't seem like this would be hard to add.
Apart from the convenience, I think this is important for deeper reasons. Programming, and thinking "like a programmer" are as much or more about reading code as writing it. Seeing other people's results can give you ideas and inspire, but seeing how they did it is going to be a huge benefit too.
A suggestion for Scratch itself is to get rid of the traditional open/save file management. Alan Cooper in About Face 3 makes a good case for why open/save sucks. I never have to "open" or "save" in Lightroom. Gmail and Blogger save automatically. I don't have to pick/navigate to a directory in Google Docs. In a product for kids especially, you could avoid a bunch of issues by saving automatically to a standard location.
Finally, it's too bad Scratch is so rigid with respect to screen/window sizes. I can understand why they did it that way - it's a lot simpler than trying to use vector or higher resolution images and make things resizable. And for educational purposes maybe it doesn't matter. (Although I notice a number of people wanting to run it 800x600.) Nonetheless, it was a bit disappointing when I ran my program full screen for the first time and got a jagged grainy image (as a result of simple resizing of the low resolution stage). Maybe I'm just spoiled by things like Mac OS X's resizable icons.