The copy to device queue functions well currently, but it prevents use of MusicBee to do anything else, like find additional albums to send to the device or playback other music while songs are being copied to a device.
My thought is that you could integrate the queue into the screen shown when selecting the root of the device tree listed under the "devices" tab (see screenshot here http://i42.tinypic.com/qrzmt5.png
), such that the queue would take up the lower half of the pane and the device infomation remain above. When you send something to the device, the content pane would automatically bring up this device info / transfer queue view, but one could navigate away from this at any time to do other things. If you wanted to get fancy, you could give a percentage indicator to the right of the devices name under the "devices" tab on the left so you could see the progress of the transfer. In the device info / transfer queue screen, you could also give indicators in a column for each track to see it's status, e.g., waiting, converting 20% . . ., transferring 20% . . ., done, error, etc. If you want to see a more visual example I can send some screenshots of how Winamp handles copying to a device.