I finally kicked Siruis XM to the curb at Christmas and subscribed to Spotify. Now I get to listen to more than the 5 same songs XM played every day.
I'm an early subscriber. I graduated high school in 2000 and for some reason, I received a subscription to Maxim. In 2002, Maxim (unsolicited) sent me a portable car XM Radio that included a one-year subscription. The promotion worked -- I still subscribe to Sirius XM (SXM; I still receive Maxim, too, although I've never subscribed, expressed interest or paid a cent for it). You can negotiate the price to $60/year, or $100 for the "all access" (which includes Howard Stern and premium sports content).
For some, Spotify would be a great idea -- SXM's music quality is terrible, their "commercial free" music seems to play too many commercials and their song selection sucks. However... Spotify, nor any other service, comes close to matching the spots and entertainment programming that SXM offers. In an era of unlimited data and free podcasts/etc., this may not be necessary. However, I enjoy listening to the news and sports simulcasts. For $8/month, I can't complain. Plus, here in Southern California, we have long commutes (time wise, not distance wise) and after a few days of steaming, your wireless provider will decide to throttle you.