By default when running OS X Lion there isn’t a keyboard shortcut to Launchpad. You could use a trackpad or a magic mouse, but what if you don’t want to buy one? Keyboard shortcut.
Launchpad is something I could use to avoid going to the dock for anything (Alfred has been updated and works with Lion). So if I don’t want to depend on Alfred (which totally rocks), Launchpad is great for finding an application when I forget it’s name or isn’t properly indexed by Alfred yet.
Go to System Preferences > Keyboard > Keyboard Shortcuts. Click on Launchpad & Dock. You’ll see that Show Launchpad is selected but there is no shortcut associated with it. In a fit of usability awkwardness (very un-Apple), it’s not clear how to set the shortcut. Double-click to the right of the row below the dock hiding shortcut, and an input field will appear. Perform your shortcut input there (I chose to use CMD-OPT-L). It’s set and will trigger now.
I’m not sure what genius thought that double clicking into a white area would be discoverable, but there you go. Launchpad on demand.