Wireless Enhanced 911 (location info for cell phones) was supposed to be implemented in 2001. It's kind of sad that here in 2008 it's still considered an experimental technology that they only thought to try after 27,000 calls from the same number.
Twice when I've called 911 on a cell phone, the rescuers went to the wrong location first. Once it was my fault for giving a wrong address, and the other time it was their fault for misinterpreting me.
I called 911 a third time recently, and this time I learned my lesson... before making the call I got an address from my gps and then while on the line I walked around looking for a physical address to confirm. It was hard to take the time to do that when the guy was screaming and spasming from what I later learned was anaphylactic shock. But in the end help arrived quickly.