To reinstall Cydia on iOS 5.1.1, you usually do not need to restore your device. You can run the original jailbreak tool you used, such as Absinthe or redsn0w, and ...
In case you doubted that an iPad jailbreak was imminent, this gorgeous little image posted by hacker extraordinaire George Hotz should prove the point: Cydia running on the iPad. Now stop being coy ...