This week's book giveaway is in the Other Open Source APIs forum. We're giving away four copies of Storm Applied and have Sean Allen, Peter Pathirana & Matthew Jankowski 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.