When reading this thread on the APEX forums about Session State Protection in APEX, I found a good tip of Scott Spadafore.
I didn't use this feature that much before, but it can be really useful to prevent users submitting the page more then once (for ex. when they hit the back button)!
Here's a screenshot how it looks like in APEX (in the Attributes of your Page)
- Yes - Allow page to be re-posted
- No - Prevent page from being re-posted