Some random thoughts:

The problem with metering MP3 traffic is that it's too easily hacked or spoofed. It's easy to disguise a MP3 file as something else.

That said, I've sometimes thought that a performing-rights org that monitors P2P traffic can impose fees on ISPs that allow such traffic, much in the same way ASCAP/BMI monitors radio stations and their playlists. The fees go to artists (labels, more likely), and the ISP compensate by tacking on a "P2P surcharge" to their customers' bills. (And if the customers don't like it, they can go find an ISP that doesn't allow P2P traffic.)

Consider this: out of a 1000 CD pressing, roughly half will be given away anyways (to the press, radio, booking agents, giveaways, "friends and family," etc.). That's assuming you have any sort of marketing plan. These are *whole records* we're knowingly giving away, people -- tell me again why I should be worried about one or two songs leaking out on some P2P network?

Even if those one or two songs are extremely popular and downloaded by millions, well...that's more people than I would have reached if there were no P2P to begin with.

I'm betting that the vast majority of JPFolks participants are largely unaffected by P2P filesharing. But I understand the concern, particularly over the precedent that will be set in the months and years to come. The days of ubiquitous broadband and wireless are fast becoming a reality.