Didn't save Lion app? Don't panic!

I wrote to iTunes re my disappearing lion app after installation and they sent me back this re-assuring email.

I am happy to let you know you will not have to pay for “OS X Lion” again if you need to reinstall your hard drive as long as you are signed into same account that you used to first purchase it, which for you was the account “jspringate”.
You can re-download apps you have purchased from the Mac App Store without incurring additional charges. To learn how to re-download apps on the Mac App Store, please refer to the steps in this article: