I use the Shuffle on my Street Glide too. Just be careful downloading music. Mine picked up a virus and messed up two computers. I'm glad my bike didn't get the virus and start running like a moped...haha.
I used a Shuffle for a while but switched to a Sirius receiver hooked up the same way. Pack the Shuffle on trips In case the Sirius or the radio craps out. Stick the Shuffle on the dash using a small velcro dot. That way I can use it with the radio or with earphones.
I agree with Radio Shack they sell a 6inch that works great. I velcroed mine to the bottom cap of my fairing. Certain Radio Shack sells gray and black took me a few shacks to find and black one.