Hearing reports that Revit 2012 software is available in some markets via the subscription center. Might be worth checking during the next few days to see if it becomes available in your market. As of tonight I'm not seeing it here yet.
The rumored release data, meaning "boxes" shipping is April 11th. That means, if the past is any measure, that the online access to it will be some days prior. Essentially once the final compiled version is turned over to the media preparation side of operations it can be posted online. Just a matter of file transfers, and web page preparation and voila...the download "meters" go wild for a few weeks at Autodesk!