I got sirius a couple of months ago. I will NEVER switch back. I paid a year up front and got a month free. For the hour each way I commute to work, 13 bucks a month is worth it.
I agree - $10-15 a month for sat radio is fine with me, provided they have no commercials, deep playlists, and a strong non-music lineup. Sirius wins the XM vs Siruis comparison to me, hands now.
I am just waiting for their genuine handheld/walkman style unit. XM announced it a short while ago and it looks awesome (includes 5 hours of digital recording, too, for timeshifting). When Sirius comes out with a comperable model, watch out!!!