After several delays and false starts, Slacker Media, the free Internet radio service, has finally released its much-hyped handheld media player, the Slacker Portable. The idea behind Slacker is pretty cool: Tell the service what kind of music you like and it will introduce you to similar new artists and give you musician bios, thereby broadening your musical horizons. The player uses Wi-Fi (or a plain old USB connection to your PC) to load customized "channels" that you create online and refreshes them with new music every time the player connects to a network. To clarify: The player loads wirelessly (it doesn't stream), so you don't need to be within the reach of Wi-Fi to listen to your tunes.