For very well known sites I doubt a typo would create good click through very well. Each time ive gogle or hoohle ive instantly notices its not google and typed the correct address on the address bar.
I think the best typo's are sites people rush to view over lunch time. Times when most people arnt allowed to surf so in a rush. Midstream sites so you still have the traffic but not the mass highstreet names people instantly correct.