I noticed this disruption last night on the way home, but figured it was weather or sunspots or something.
XM Restores Radio Service:

XM Satellite Radio restored service Tuesday after a software glitch knocked out the signal from one of its four satellites and disrupted service to many of the company’s 8 million subscribers for about a day.

The problems began around noon Monday, the company said. They initially expected to fix the problem after a few hours but service remained disrupted for about 24 hours.

‘The problem occurred during the loading of software to a critical component of our satellite broadcast system, which resulted in a loss of signal from one of our satellites,’ the company said on its Web site.

So they pushed an upgrade without, it seems, adequate testing, and it failed as soon as it was deployed. Whether your software enables sharing your favorite iTunes playlists* or broadcasting 170 satellite radio channels to millions of subscribers, it’s important to test before upgrading!

* plug