I just got a friendly BBM from bluemax413 that beta os18.104.22.16811 is now available for us who want to play with the new PlayBook operating system from RIM. It has Adobe Air 3.0 and some other goodies. They did leave out all the stuff we are really waiting for like email,calendar, and contacts. You can sign up and get more details here here.
DISCLAIMER: By installing this OS you might lose some of your information and applications. Please understand the risks of installing/running a beta operating system on your playbook.