Definitely get Chris Pirillo in. I was listening to some of the feedback he was giving Shanen Boettcher at the blogger lunch in Seattle on Tuesday, and he had some solid, concrete ideas for improvement. Plus, he's not hesitant to be critical when
Brandon Paddock also posts lots of good suggestions and feedback on his blog. I think he'd be another great choice, especially in the search and organization space.
Marc Orchant for feedback on pen-based input in Longhorn is pretty much a no-brainer. He really knows his stuff, and his blogs are a joy to read.
I'd love to be there myself. I attended WinHEC and the x64 launch last week, and it was a blast. I do meet the core "requirements" - been a regular blogger for two years, and I've been passionate about computers since the age of 8. =)