This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
This is definately a frequently asked question. There is no way to disable the back button. A much better approach is to make your web application happy to serve any of its pages based on the current state of its data model, and mark any dangerous pages as not to be cached.