I've read the advice, "don't break the back button" from multiple sources. For content-based browsing I agree with this 100%. Does the same advice apply to web applications? I feel that it is still valid for web-app pages that simply display data. Once posting forms, AJAX, and logged out sessions become involved, the back button might result in unexpected behavior.
Is this advice relevant for a highly-interactive web application?
Here are some articles that speak to this topic: