RIM has just released a new version of the BlackBerry Tablet OS SDK for the BlackBerry PlayBook. The new version was added to include support for Adobe®Flash Builder 4.5, support for Windows 64-bit and Linux.
There is also this nice note on the Tablet SDK page:
Coming soon: support for content and applications using Adobe Flash 10.1 and HTML5 with the BlackBerry PlayBook Simulator with the BlackBerry® Browser.
You can download the updated SDK beta at this link on RIM’s website. Let us know if you give it a spin. Personally I am waiting for the HTML5 WebWorks SDK.