From a flash actionscript side, printing the page output from the flash webviewer is straight forward. However, there is no way to do this currently from the web/javascript side of things. If you need printing now, you would have to download the flash webviewer sdk, and expose some actionscript functions through the Flash/AJAX bridge so that you could print through javascript, or add a button to the Flash WebViewer ReaderControl toolbar.
This is on our plan, hopefully for the next release, but I expect this to be still a few months away.