It hasn't affected mine.I've only had the car a few weeks, and have no problems with the XM. We had a rental car a few years ago with Serius SAT radio, and every time you changed directions (almost), you would lose the signal. They have either improved the system, or we just had a bad rental car. So far its all been just fine with the CT.
I am thinking of going to a Sharkfin antenna. I have one on my Prius, and have been very happy with it (without SAT radio), and wonder if it will affect the XM, or is that on a different antenna?