Wow, that was quick. Here's what Autodesk is saying about this release coming out tomorrow (in Canada anyway):
The Revit Building 9.1 products deliver the best possible information for decision making by increasing support for interoperability and enhancing coordination and quality, while optimizing workflow across the Autodesk Revit product suite. (this is an interchangeable blurb Autodesk uses when it a. doesn't have anything to report b. doesn't want us to know.)
Revit Structure 4 contains many new modeling features, pre-cast concrete and steel content, analytical tools and enhancements for reinforced concrete documentation. Of particular note are the TrussWizard (available only to Subscription customers) and the one-click beam system creation feature. (sound interesting)