While a micropayment system is intriguing, there's another consideration - longevity. (Well, there's international or near-international coverage, but that's for later.)
PayPal is in process of killing off its existing Plugin process(es). One of those processes, one I've used since its inception, is single-use or single-payee (recurring billing) cards. After two-plus years, they've presumably decided it's not sufficiently profitable, so it's getting eighty-sixed.
That's unsettling for me, considering the number of commercial sites get raided of consumers' financial data.
Same thing could happen with a micropayment system: folk come to depend upon it, then it gets retired - for perfectly understandable reasons, but that doesn't help anyone who might have come to rely upon it. If their business model is even moderately dependent upon micropayments, they'll become collateral damage of someone else's (in this case, PayPal's) valid business decision.