Plugging in a Sansa Fuze (running Rockbox) while Amarok is running results in no device detected by the OS (Kubuntu 11.10) or Amarok (2.4.3), at least as far as I can tell. Shutting Amarok down and re-plugging the Sansa makes the device accesible . . . until Amarok is restarted, at which point the device isn't detectable. Haven't tested with any other media devices
Please test with the latest beta. Final version will be released soon. http://amarok.kde.org/en/releases/2.5/beta/1