Help and related documentation for the three Revit products is now available on the web. The online help can be accessed from the documentation pages for each of the product centers on autodesk.com. Here are product specific links:
PDF and html formats can be found.
Here are more direct links to Revit 2010 html help (English):
Those who grow weary of telling others too many times to "read the manual" can now share a specific topic with your colleagues via a hyperlink.