Another lefty here!
I'm pretty ambidextrous, due to the 'Shawns sister effect' where I broke my left wrist and was forced to use my righthand for a period of time.
I tend to do different things with different hands, I write with my left, play darts with either, throw anything else with my right and play pool (poorly) with my right. Some people find it strange because I pick up and use knives and forks either way round.
Dunno about Vinces theory about turning, from what I can remember I never had a preference when riding a bike. I do, however, prefer turning left in my car for some reason!