I have already been using ExtJs 4.0-Beta3 for the last couple of weeks. And an hour earlier, I occasionally went to the Sencha site to check one of my posts on the forums. And the surprise was waiting there. ExtJs 4 had been launched today.
I immediately downloaded the release version for ExtJs 4 and updated the latest build to one of my projects where I was using ExtJs 4 Beta 3. Separately, I configured the accompanying docs to run over IIS 7 on my Windows 7 machine.