Tom Moon waxes philosophical in the Chicago Tribune on the almost-infinite interchangeability of music facilitated by the iPod, where mixing and matching can turn into a sophisticated exercise in music appreciation:

Something radical happens when you disengage from physical discs and tapes, when you collapse the distance separating "rock," "jazz" and "world" in the record stores and view the collection as an ocean of possibility. Daily life gets a different kind of soundtrack, endlessly mutable and instantly reconfigurable. Sometimes it's pure utility: What you need going home on the subway might be many decibels away from what you need when you're waiting at the dentist's office. Sometimes it's pure perversity - Booker T's greasy soul into some up-tempo Basement Jaxx electronica freight-training into Joco Gilberto singing "Quiet Nights" at a whisper.

I loaded in an hour of Miles Davis gems, culled from probably 18 discs. Then a Brazil mix including more than a dozen artists, then a "new garage" mix centered on the White Stripes. The discs and their cases would have filled a large backpack, and even if you did carry them around, you'd never be able to create a mix without expanses of "dead air" while stopping and reloading the CD player.

But it was a jazz guitar mix that demonstrated the music-appreciation value of these devices. Starting with selections from the recent box of pioneering electric guitarist Charlie Christian, I put together a slapdash, incomplete evolution of the guitar through jazz history - some Wes Montgomery, Jim Hall, Tal Farlow, Grant Green's 1961 "Sunday Mornin' in its glorious gospel-soul entirety, some vintage Pat Martino, early Bill Frisell, Pat Metheny.