[citation][nom]matt87_50[/nom]should just be pay by the byte...now THAT is fair!most people who cringe at the idea do so because they assume that means "expensive" but it doesn't have to be. the important thing is that its fair.[/citation]
The problem with such a system is three-fold.
1) The major ISPs seem to have royally incompetent metering systems. As someone that had to use Verizon's wireless Internet (5 GB cap) for two years because of where I was living (older house with a myriad of conditions that didn't support even rudimentary dial-up service), it was astounding to watch their online meter utility. It updated approximately once every three days and was a total crapshoot on whether it accurately measured usage. The measured accumulated usage regularly went down by not insignificant values (worst example: 675 MBs--more than 10% of the monthly usage--was suddenly available again, and it stayed that way the rest of the month). Anyway.
So, let's assume that isn't going to be a problem and they have an undisputed method to accurately and precisely measure total usage capable of providing an instantaneous "snapshot" of the accumulated usage at any given moment. Okay: Does that separate incoming and outgoing data? (My cable connection uploads at 1/10th the rate it can download--is outgoing data suddenly going to cost 10x more than incoming data, per-byte?) Can it "sniff" the packets to know what each is being used for? (Beyond the privacy issues, are gamers going to suffer "premium content" pricing? How about Hulu users? Or YouTube users? How about if I use Google rather than Yahoo to search?)
2) "Per-[unit]" pricing always has an "access" fee. Typically, such fees are often described as being for "Service Availability and Maintenance" or other such nonsense (also known as: subsidizing the costs of infrastructure). Problem: What would be the minimum scheduled payment for "access"? I can just about guarantee you it wouldn't accurately reflect the actual cost of maintaining the connection.
3) "Per-[unit]" pricing rarely results in a "fair" system. All that nonsense about the "high-demand" users you hear now? Now instead of artificially increasing the cost of access, you're going to see the per-byte cost increase to "meet the demand" of said users (who may as well be equated to mythical lore at this point, akin to bigfoot, a sane follower of Palin, or the Loch Ness monster)--it's the same shit, just a different pile. But getting beyond that... How do you define a "fair" per-unit price? If we use the per-MB overage cost of that Verizon Wireless Internet I mentioned above, you could possibly expect $0.05 for each MB (at the time I used it, the overage was $0.25--before that, it was $0.49). What happens when Windows 7 suffers a particularly nasty series of attacks and you suddenly have to download an unexpected 500+ MB of patches for three PCs and a laptop? Do you really want to pay another $100 that month (2000 MB @ $0.05 each) just because of some viruses and Windows?
Sure, maybe Grandma&Grandpa are now only paying $20 for access and $1.25 to check their e-mail once a week...but the user who actually, well, uses their connection is still rocking the standard $50-100 currently paid, at best. At worst and the most likely scenario? That user is still going to pay more than they should have to. All that's changed is now the "high-demand" user (however that's defined) has to pay more for their service. That's it. Your bill wouldn't be any more transparent under per-byte pricing than it is now.