Possible Duplicate:
Manually clear saved question drafts
When editing a post there is no clear way to discard changes, one can click the Return to Question/Answer
link but that's not entirely intuitive and it prompts for confirmation to "navigate away from page".
I would suggest adding a Discard Edits button which I don't think should prompt for confirmation (since it's an explicit action).
The ideal would be to discard edits without prompting but add a Gmail style link to go back to editing from where you left off.