The first was launched recently and 15 more are anticipated by the end of 2006.

http://www.newscientist.com/article.ns?id=dn8051

Stronger signals and more accurate clock are a few of the improvements. (Accurate to within 8 nanoseconds per day).
Also going from analog to digital. Uh, is a nanosecond quicker than the blink of an eye? <img src="/images/graemlins/smirk.gif" alt="" />