Great upgrade with many welcomed features.
I tested it on fresh installation. Works smoothly but found some issues and shortcomings:
1. Accessing the Plug-ins page from the back-end shows blank page
2. Widget templates section is not operational
3. Tags management are not easy or powerful enough
4. The Users Management has not changed much from the previous version: no news/articles integration with user accoutns as promised, no security image for user registration, no advanced editing/management options, no newsletter integration, etc., unless you plan to make it as separate plug-in
5. Admin back-end showing "Done, but with errors on page" in IE7/8 in all pages
We are all waiting to see even more options and surprises in the final release.
Keep up the good work