This "solo drag @ level 3" strat is funny as hell.
It happens in at least 60% of my ranked games. Thankfully, I've picked up on it so I can usually stop it. In my last game I got a solo kill on a nunu who was doing it xD
Always ward that dragon pit at 3:30 on if you're facing a WW/Nunu/Vi/Udyr... There are a lot of jungles that can solo it.