Actually the only thing I ever did like about Sirius was the sound quality- it's between CDs and FM in my opinion. Of course, that was when the DJs weren't jabbering on on top of and between songs, that is.
Sirius also has a superior satellite setup, where they have three sats in constant orbit, as opposed to a geostationary orbit like XMs 2.5 sats (one of the three's gonna replace a failing second sat):
Of course, this is better for moving vehicles like cars, but at the same time there's going to be times you're not going to get a strong signal. When the Sirius sat that's not in the CONUS orbit, it's turned off and recharging its batteries at the same time. I hear Sirius' CODECs are better than XMs, as well.
Between the technical superiority and the lack of issues with the Infiniti Clarion satellite recievers (the Sirius units don't have the 10 character display limitation nor the "loading 'till restart" issues of the XM recievers), it's a nice setup- too bad Sirius programming bites, and I can't wait to get rid of it!