Even after running it for over a fortnight now (I think?) I only just found out how to submit feedback about my experiences. Surprisingly, this beta isn't covered by the new Microsoft Beta Client tool that is used for Windows Vista. Instead they use a program called "Send a Smile".
As gimmicky as it looks and feels, it's actually pretty nice to use. It adds two little faces to your notification area – one happy and one sad:
When you click either one of these buttons it automatically takes a screenshot, gathers all the version information and platform data that they might possibly need, gathers some free-form text to describe the experience you just had, then sends it off to the product team. Of course, if the screenshot isn't perfect then you can refresh it, or if it's irrelevant you can choose not to send it.
I wonder if this approach to the problem is another case of Microsoft being the out-of-touch parent?
Of course – they couldn't stick to the nice simple "Send a Smile" name could they – under the covers it's called the "Microsoft Office Information Worker Feedback Tool".