Here is a summary of a Air Force report on difficulties replacing aging GPS satelites. They are behind schedule and predict the probability of keeping a 24-satellite constellation in orbit drops below 95 percent in 2010, and could drop as low as 80 percent in 2011 and 2012.

This doesn't seem to be that big of a deal but it is a reminder that you can't always count on technology (as if we all need that reminder).

-Blast