I make this a habit when developing web applications to always return a redirect from form posts. It provides for a better user experience - users will often leave a result page (like an order summary) and then use the dreaded back button to return to it, sometimes saying yes to the 'resubmit form data' question.

Responding with a redirect to the initial POST avoids this (in most cases), and the aforementioned multiple submission issue. You don't even have to resort to javascript to prevent them from using the back button :)

It's just a better experience for the user.

Kyle