Following the virtual launch on May 12th of Project 2010, the Office Content Publishing team published the content to help use Project and Project Server 2010 on Office.com. Currently, end user documentation for Project Web App can be found on Project Server 2010 Help and How-To page and includes:
What's new in Project Web App
Getting started with Project Web App
Up to speed with Project Web App (video series)
Getting started articles for each of the following roles:
Discontinued features and modified functionality in Microsoft Project Server 2010
More Info: Project Server 2010 Help and How-To
Also, end user documentation for Project 2010 client can be found on Project 2010 Help and How To page.