four weeks ago i began a subscription to Sirius radio.
WOW, as a music lover, its a god-send. I'll list pros and cons based on my experience.

Satellite receiver = Sanyo CSR-10 (comes w/ home and car kit and FM mod built in) $150
Receiver = Harman Kardon AVR-525 - 7.1 receiver for controling 2 zones

Pros
  • 65 commercial free channels
    scrolling artist and song (some with year released)
    wide range of music categories...from bluegrass to old-school rap
    using 3.5mm plug..you receive CD quality sound
    Ability to plug into audio input of your AV receiver so you can use all surround formats
    Ability to use AVR to fine tune your sound like in PLII or NEO:6 (Bass management)
    Using AVR, listen to music while watching TV or any video source (Playstation II)
    Online streaming of all music channels (XM doesn't offer)
    Real DJs...like back-in-the-day type (no song sponsored by 'Ben Gay' type crap)
    NFL network channel
    NFL Sunday Ticket (Directv charges $180)
    Audio output to calibrate with your system
    Small and portable thanks to built in FM modulator


Cons:
Other than music channels - do have commericals... like ESPNews,NFL channel, CNN, etc
Only 20 presets (imagine filling 20 with FM radio)
FM modulator emits static if you have a local (strong) station. Trail and error to find best sound.
To get CD quailty in your car, must have a deck with an AUX input.

Since this is a HT forum, i'll speak to what's important. Running satellite radio through your AV receiver provides many options and lots of fun. Converting to 5.1 formats and tweaking them can bring some great sounding music that fills a room.
Music quality varies...on channels that play newer music, digital quailty. Older music sounds like a inferior CD mix. Overall, majority are superior to your best FM station.

disclaimer:
I don't work for Satellite Radio, but as a music lover, i can say 'do yourself a favor' and research it.

Sirius gives you a free trail online, so you have nothing to lose and 65 music channels to gain.