We bought my girlfriend's dad the Sirus S50 for his company car (we'll remove it when time comes). It's portable just like the S100. For $49 (+subscriptionof course) it came with the car kit and all the portable accessories. I think it has all the same features as the S100. It took about 15 minutes to install it and activate.
He travels a lot in his car so the thing should be useful.
If the subscription rates wasn't so high (I think it is), I'd get one. But I'm too cheap, and my SLVR phone holds the tunes I want without me having to carry around one more piece of electronic gadget.
Enjoy your present, Bell