Yesterday I picked up a Skydock at Best Buy. It took less than 10 minutes to set up and activate the subscription. I added it as an additional subscription.
I've only used it for one day, but I am extremely happy with the product. Set up via AUX plug, the sound is crisp. When I tested the FM capabilities, I was a little disappointed with the Skydock - too much crackling and it sounded like I was listening through a tin can. The software is easy to navigate and set up; even the ticker is readable ( the choppiness of the ticker on other plug and play units always bothered me).
Right now, the only big negative is due to the smaller size of the Skydock is the placement of the unit in my car, a PT Cruiser. The power plug is lower on the dash and in order to change channels or press "tag," I have to look down for a few seconds; not the safest action when driving. This is, of course, more of a PT Cruiser problem (why did they put the cigarette plug so low) than it is a Skydock problem.
In the future, I hope XM somehow makes a home dock for the unit and if, by the grace of God, some sort of remote could be paired with the software, thus making driving a little safer.