I read a report today that stated that SIRIUS stock jumped nearly 18% following the Stern news. Say what you will about him, but that is pretty remarkable. Especially considering that he won't be on SIRIUS until early 2006.
XM carries a few heavy hitters of its own, so I'd be curious to know how the current market share comparison shapes up. From where I'm sitting, it seems like XM is definitely much more "visible" out there. I had never heard of SIRIUS before Joe Black told me about it, and never saw anything about it at a retailer until much later than that. Times are changing, though.