While everybody was gawking at the news coming in from the WWDC 2011 Stevenote today, Apple silently slipped in an update to the iOS iTunes and App Store apps. The update, which was made on Apple's servers, adds a feature that was described in the keynote -- the Purchased button.
As you can see in the screenshot at right, looking at Updates in the App Store app now displays a Purchased button. Tap on it, and you see a list (below) of every app you've purchased. There's a tab displaying all purchased apps, and another showing just those that have been purchased but are not currently installed on the iOS device.
The apps that you've purchased and haven't installed (or that you've removed) display a little cloud button with a downward-pointing arrow, indicating that you can tap that button to install the app on your device.
For iTunes, the Purchased button is located in the bottom toolbar (see below). A tap displays all songs that you have purchased, recent purchases, and then an alphabetical list of every song purchased by artist. When you find a song or album that you own, but that isn't currently on your iOS device, a tap on the cloud icon downloads it immediately.
The change isn't immediately noticeable to the user who only occasionally visits these apps, but it is going to be very useful for owners of iPads, iPhones, and iPod touches who might need to remove apps or music to gain storage space, and then want to reload their content.
Update: One more little detail. When you're in iTunes and music that you've purchased is being downloaded, there's a small red indicator that appears down in the bottom right of the toolbar (below) and counts down as the songs appear. Cool!