With respect to the API, the http://www.autodesk.com/developinventor website has been updated with the information for Inventor 2011. There is a PowerPoint presentation that goes through the new API features and also a set of demo files, including sample code, that demonstrates many of the new features.
To learn about new non-API functionality in Inventor 2011 you can attend a virtual event that Autodesk is hosting. It’s Monday, April 19th, 2010 from 7am–2pm Pacific time. Register for this event at http://www.autodesk.com/seizetheopportunity