I've had XM since late '03, and I don't see myself going back to regular radio. Sirius is still a few million subs behind XM, and their stock price is around a quarter of the XM price. (as of this post, XMSR is $15.34 and SIRI is $3.78)
SIRI locked into a HORRIBLE deal with Stern. While they did get a bump in subs, it was not the HUGE payoff they had expected. (Not trying to start a Stern fans vs haters discussion--just simply pointing out SIRI did not get the huge number of subs everyone expected them to get when he moved over)
Overall, though, BOTH companies are making HUGE DOLLAR deals for exclusivity that they can ill-afford. From MLB to Nascar to Stern to NFL and more, both companies are fighting each other rather than making the fight about Satellite vs. Free Radio. A merger would be the best course, in my opinion, as they would be able to consolidate and take the real fight to the technology much like cable TV did in the 80s. When cable first came to your area, you didn't have two providers fighting for business and fighting over content--you had cable TV or you had an antenna on your roof. It's only after cable dominated the market did you see alternate providers begin to appear. In my area, though, I have the choice of 1 cable company, several satellite companies or antenna.
Sat radio needs to stop fighting each other and pit the satellite vs over-the-air technologies against each other to be truly effective.