Well, quite a lot actually. The fact that the official agenda is completely empty (they're not even telling us who is doing the keynote ontheir website) leaves us with wondering what will happen. Of course, this means that people are getting more and more anxious to see what is going on and the blogosphere is filled with rumors. Which ones will be true is something we'll learn next week.
I expect we'll get a lot of information about Jupiter. The new development platform is something that interests me a lot. I love doing XAML, both in WPF and Silverlight and I am happy to see that Microsoft is going to make XAML a first class citizen. After all, a large part of the team that build WPF is now part of the Windows team, meaning it's going to be an integral part of the OS.
Although I am not really a web-developer, I am also curious to see which direction Microsoft is going with HTML 5. The tooling is already out there; you can use VS2010 perfectly well to develop HTML 5 websites but I expect to see a lot more on that area.
And of course there's going to be a lot of sessions on Windows 8. Nobody knows the state of the project. Some say they only have an internal version ready (a milestone version), others expect atttendees will get a beta of Windows 8 (I doubt that, but who knows?). Since Build Windows is the marriage between PDC and WinHEC there's going to be a lot of sessions for developers AND for IT Pro's. I am sure I will come home with a lot more information about the next platform.
One thing is sure: it's going to be a great conference. Never before has Microsoft held an event that has been so secret about it's contents. That leads me to expect some big surprises. After all, what's the point of keeping things a secret if there's nothing to tell?
Stay tuned for more information!