As more of the Internet becomes mobile (and you can count on that) more of the "radio listening" will invariably follow.
If that listening is to a stream you will get all the metrics you need from AndoMedia or sources other than Arbitron. They will be 100 percent accurate and will have a variety of targeting details unavailable from conventional ratings data.
Whether that listening is to a stream or "over-the-air" you can assume that folks are generally using the same earbuds they're using to listen to mp3's if they're listening on a mobile device (unless it's plugged into their car).
But wait a minute.
If PPM works off an audible signal (which is does) and an additional gadget is required to go between those earbuds and the otherwise inaudible mp3 player on their other end, then the precision of PPM depends (among other things) on how many folks actually go through the cumbersome and inconvenient process of attaching a clunky middle-man unit to their lovely new Zune or iPod Nano.
So what does the rise of radio in mobile environments mean for our attitudes about PPM and the attitudes our advertisers will have about PPM?
If I were an advertiser in a world of rising mobile "radio" usage, I would place more confidence in verifiable streaming metrics than in any collection of sampled data produced by a methodology which required some Rube Goldberg contraption dangling from my hip and installed at my discretion.
Sure, it's just an attachment connected to a meter. But there's nothing passive about hooking and unhooking that up.
And history shows that any time we add more steps to that which doesn't require them, consumer compliance is always an issue.
What do you think?