Since I posted this, over a year ago now, my left hand has become dominant. I've been addicted to this goofy game for over two years now.
When I first started playing with my left hand it felt so awkward. My right hand wanted to rip the controller away. Now it's the opposite. Recently when I play with my right hand it's my left hand that will be resting on my hip, wanting to take control of the mouse.
Since the beta was released I played so much that my left wrist is now sore. so I switched back to using my right hand bout a week ago, and I find it's much improved.
So now both hands are competent

However they've different styles of play. Right hand is by the book - work on matches, clears, and holding the chain. Usually avoid white blocks. Left is completely loco - grab everything in sight, and has an appetite for white blocks. Right hand is consistent, left hand go for broke - usually comes up short, but occasionally scores big
I'll have to post some videos sometime, showing the difference on the same course. That'll have to wait until I get a faster computer..mine slows down too much using frap.