Rather belatedly, I note that the first web update of Revit 2011 was released in the beginning of this month and can be downloaded from the public Revit product pages:
Here is the list of the API enhancements, which is the same across all three flavours:
Elements will now be properly joined when the ExternalCommand concludes when using automatic regeneration and automatic transaction.
ExportImage(ImageExportOptions) no longer throws an exception when given a set of views.
ElementParameterFilters now operate properly against ElementType elements.
Improves stability when saving a family and there are event subscribers for Save or Save As.
Closes the Family editor environment after loading a family via the API.
Improves stability when using selection APIs to pick grid elements.
Dynamic Model Update: GetChangeTypeGeometry() now triggers properly when active type is changed.
Improves stability for Dynamic Model Update: when registering updaters and more than one application is registered.
The new API SunAndShadowSettings.CalculateTimeZone() uses Revit�s mechanism to calculate the time zone value for a given latitude and longitude. This calculation is more accurate than the results obtained from City.TimeZone.
Improves performance of display of Analysis Visualization framework when Hardware Acceleration is on.
VSTA is now allowed for multiple concurrent sessions of Revit; editing the same module by two sessions is prohibited.
VSTA: Document-level macros no longer become corrupted when the document is workshared and the macro is edited by more than one concurrent session.
Improves stability when calls to NewFamilyDocument() and PickObjects() are used in sequence.
VSTA: Revit no longer prematurely exits when opening a project containing corrupted macros.
The Idling event no longer generates a journal comment for each invocation.