Perhaps you've read about or even visited either Slacker or the Pandora on-line radio sites. Both sites have a variety of on-line stations but also offer the ability to make a custom station just for the listener. Pick a style or an artist and you decide how deep the library will be, which songs are your favorites, and what artists to include in the mix.
Now they also offer portable players. Pandora has units that take a stream from wireless connections wherever you can get to one. Slacker is a little more interesting as it uses a cache system to load up the player quickly then allow you to keep listening even while you are away from the stream. Slacker is also working with a satellite system so you will be able to listen on the road. Slacker has negotiated rights to the music on the system and are not burdened by the Sound Exchange royalties world but Pandora could be in trouble as streaming fees increase. There are some unique limits - both offer the opportunity to skip a song and move ahead but only 5-6 times in an hour. With Slacker you can purchase a premium subscription and skip as much as you want.
Ok fancy tech, but how well does it work in the real world. I decided to put together a station myself and see how well it works. I was a big fan of the Byrds and it's been years since I spent time with their music so I chose them as an artist to center my station around.
When I punched up the Byrds artist station on both Pandora and Slacker it was a unique adventure. The Byrds show up about every 15-20 minutes or so on the Byrds station on both services. On Slacker the rest of the selections are from all kinds of bands that were either influenced by the Byrds/CSN world like Tom Petty or REM and the rest are bands either from the era (Beatles, Grateful Dead, Airplane) or that share a folk style (Dylan, Fairport Convention, Lovin Spoonful). You can set the mix to be more obscure or familiar or center it on an era (but here are no currents or recurrents to work with). On Pandora the mix was very different with tons of new Indie bands (some we've never heard of from indie labels) in the mix and very few 'era' moments.
You can also create a station so I tried to build My Byrds Radio. By selecting songs as favorites I was able to build a list and then set the station to mix in those favorite songs either once in a while or a lot. But, I had to listen to each song all the way through - a long process just to build a Byrds station. Trying to steer the station away from the long Fairport Convention songs or the Grateful Dead jams I didn't want was going to take forever. On Pandora it was even worse as most of the non-Byrds songs were indie bands even a rock programmer couldn't ID that sort of sounded like alt/pop versions of Byrds songs. Sorry I got other things to do - it would be better just to go to my CD collection rip off the Byrds CDS and a few other bands into a Byrds file on my MP3 player and sit back and enjoy.
Still it's an interesting option. It may catch on and become the next interesting application of Internet radio. While Slacker may not have Sound Exchange over it there are still issues with the system that are designed to limit the system so some fees can be collected or so you will be stimulated to go out and buy some music instead of putting in so much effort to build your own world. Pandora on the other hand will sit on the edge of its seat till the CRB decides the fee issue.
Is it a threat to terrestrial radio? Maybe but it's a lot of work to make any of these services personalized. Yes some will jump in, but they won't quit listening to us.