I haven't upgraded yet. But this is just a thought. Since Lion OS10.7 is a download from the Apps store, how do you retrieve an App if it gets corrupted? I was helping a friend re-install Address Book on their Macbook which is running 10.5. Now it was an easy re-install. Grab the system disc and locate Address Book under the Applications folder. While they were locating the files, I plopped in my MBP system disc into my computer, and saw a few things in the Applications folder. My computer came with Leopard install and a physical copy of Snow Leopard so that I can upgrade. So then I checked the folder on my Snow Leopard disc and saw more Apps in the Application folder on the disc. I'm just wondering how do we correct/fix our computers without all this info? because we do not have a physical disc.