Don't rely on the MAS to download the same app in the future -- you may be hit be obsolescence with your system! Save the downloaded app just like you would save distribution CDs/DVDs! In January 2011 I bought iMovie 11 in the Mac App Store. This was back in the Snow Leopard days, of course. While my major systems are all Lion now, and have been upgraded, I decided to install iMovie 11 on an older Mac mini with Snow Leopard. I can no longer do it! iMovie has since been "upgraded" and no longer will work on Snow Leopard. I can't download the old version from the store. Looks like the same would be true for iPhoto bought at that time, if I had done so. I can find nothing in the Terms of Service about purchased products becoming obsolete like this, and am writing Apple. Edited to add -- I bought a MBP a few months ago which came with iLife11, of course through the MAS. The store now shows iMovie 11 purchased in March 2012 instead of January 2011. That might be the root of the problem. I'll see what Apple says.