Web parts scenarios
After my initial reading of Mike's post, I was under the impression that modifying web parts without a postback was an AJAX 1.0 feature. Unfortunately, after reading his blog post, I understood that this scenario isn't supported in this release. So, you can do 1 and 3 (cross-browser drag and drop and updating contents of the web part without full postback) in the current version, but 2 (modifying web parts without full postback) will only be possible in Orcas (and this is only a possibility).