We've had Sirius for a year in both vehicles, we use the internet to listen in the house. We love it. It's what FM radio used to be before Clear Channel and all the megastations screwed them up.
We also love it because as we drive through our local mountainous terrain we don't lose the radio as we did with normal radio. But if you're in a city with tall buildings,in the country with deep forest cover, in a tunnel or stopped under a bridge you lose the satelite signal. Weather doesn't seem to bother it.
I haven't listened to a tape in the car since we installed them.
There are deals with Sirius for add on units. You pay 12.99 month for the first unit, units 2-4 for additional 6.99 total (not each) the internet service is free.
Dave