Brian describes a UI metaphor for micropayments, with a gauge indicating the value of your micropayment purse and a cutoff for the maximum automatic per-unit payment:
Now, let's consider bridging this metaphor into the micropayments world. Imagine that surfing the web is like driving a car - you'll dribble out small amounts of money over a period of time, but as long as you watch your speedometer (the rate at which you spend money) and the feul tank levels (the amount of coinage in your wallet), you are in control of your spending rates. Whether you approve every micropayment explicitly, or you set a minimum level below which requests for payments are automagically granted, is up to you. Me, I'd probably be alright with just about any site I go to asking for less than $.02 for any action I take. Anything above that, I want to be explicitly asked. My user interface has a gas gauge and a speedometer in the upper-right-hand corner instead of a throbbing "N". When my levels are low, I go visit my bank and "refill" my wallet. Voila!
That's fine so long as the majority of sites one visits all cost within, say, an order of magnitude or so. What happens if people skip around a lot? When I go from checking out Hagbard's Poetry Corner, which charges $.02 cents per page (and falls below the speedometer cutoff), and switch over to Belbo's Future's Tips Market, which charges a dollar a page, I'm going to get annoying alerts every click. If one allows customizing the cutoff for each page, the guage becomes meaningless (as much as if your car occasionally sucked half the gas tank at one stoplight). If you don't, it is annoying. Sure, $1.00 a page, perhaps, pushes the micropayment scale, but I'm sure there are plenty of folks who would set the cutoff in that range or higher. Perhaps a graphical relation-o-meter, comparing some user defined scale to the cost of the current page, so that users could get a relative feel for high rent districts (Web-rent control, anyone?), but I can see pitfalls to this appoach, too. I don't think this works unless the micropayments world standardizes on a very narrow price band, which isn't very likely, or people are found to stick pretty consistently to a given price when browsing, which I don't think is very likely either.
And yes, I am presuming a system involving transfers of digitally signed tokens of some sort. I don't think this is a mistaken presumption.
It strikes me as perhaps more useful for account-driven billing systems, where one has a contanst quanta of payment magnitude. -j -- The signal is the noise. ____________________________________________________________________ Jamie Lawrence mailto:jal@cyborganic.net mailto:foodie@netcom.com