That's where we NEED to move toward some easier way of frictionless micro-transactions that are secure, safe, and ubiquitous... how to do it is unclear, but perhaps a mega-site like Facebook could create such a thing.
Also, paypal's donate feature has existed for some time now but it doesn't seem to be able to replace ads. If anybody could implement the safe, seamless microtransaction model I'd think it'd be paypal as they have the existing infrastructure already. Either they have overlooked it or they've decided that the model wouldn't work.