Right now, I use Debit most, along with occasional Credit and Cash purchases. If any of the three options offered me a cheaper solution somewhere(even 1%), I'd use that one almost exclusively. I'm not too worried about my card being stolen - I take responsibility for my money. If it gets lost or stolen and someone empties my bank account, I will dispute it, but consider it a lesson learned. With cash, if it's gone, it's gone.
What I'd be most interested in is how merchants who run Debit transactions as a Credit(signature) will fair - will they all switch payment processors to someone who does (cheaper) debit transactions, or will they end up charging more for Debit as well? Only time will tell.
Either way, I think this is a good thing.