I don't know what you count as useable, but I have an original iPad Air here (3 years old) that still works fine for my use - some games, email, reading, and internet.
It was only this year that I stopped testing our apps on the iPad 2. It was workhorse, and for many apps was much better than the iPad 3. With the 3 Apple went to retina, but IMHO the rest of the hardware was not quite retina ready.
It was only this year that I stopped testing our apps on the iPad 2. It was workhorse, and for many apps was much better than the iPad 3. With the 3 Apple went to retina, but IMHO the rest of the hardware was not quite retina ready.