Speaking of what Microsoft is and isn't sharing with Windows 7 testers, starting on February 24, Microsoft is planning to roll out test updates for Beta 1 users.
As explained on the Microsoft Update Product Team blog, these updates are simply designed to test the Windows servicing infrastructure. They won't provide any new features, fixes or functionality for Windows 7.
From the February 19 Microsoft Update blog post:
"We do typically verify update scenarios during a Beta, and releasing these test updates will help ensure that when we need to release real updates, the process will run smoothly. There will be at most five updates....
"The updates will be offered interactively. This means that users will be notified of available updates, but they won’t install automatically. Users will need to go to the Windows Update control panel and manually start installation. They will also be clearly titled as a test update. If you don’t want to install the updates then you can right click on each update and select 'Hide update' to prevent it from being shown in the list of available updates."