Comic author Scott McCloud, who has previously written about micropayments, is now trying it out himself. Penny Arcade didn’t quite buy into it a couple years ago.
There is not a whole lot of information about the BitPass system that Scott has signed up with. From what I’ve been able to gather, you buy a minimum of $3 using PayPal or a credit card and then you deduct the small payments from your balance. That certainly seems reasonable if a lot of people sign up with this system.
I think Visa and Mastercard could corner micropayments if they wished, just by putting together a low-overhead online payment system. However, they don’t have a real strong incentive to give up their $0.25-0.35 transaction fees.