My latest Guardian column, "We must ensure ISPs don't stop the next Google getting out of the garage," talks about how the policy debate over "Digital Britain" has ignored the most important aspect of a digital nation: a fair deal on open network access.
But the real problem of per-usage billing is that no one – not even the most experienced internet user – can determine in advance how much bandwidth they're about to consume before they consume it. Before you clicked on this article, you had no way of knowing how many bytes your computer would consume before clicking on it. And now that you've clicked on it, chances are that you still don't know how many bytes you've consumed. Imagine if a restaurant billed you by the number of air-molecules you displaced during your meal, or if your phone-bills varied on the total number of syllables you uttered at 2dB or higher.
Even ISPs aren't good at figuring this stuff out. Users have no intuition about their bandwidth consumption and precious little control over it.
Metering usage discourages experimentation. If you don't know whether your next click will cost you 10p or £2, you will become very conservative about your clicks. Just look at the old AOL, which charged by the minute for access, and saw that very few punters were willing to poke around the many offerings its partners had assembled on its platform. Rather, these people logged in for as short a period as possible and logged off when they were done, always hearing the clock ticking away in the background as they worked.