The reason I decided against this was after googling for info, I found this site :
http://priuschat.com/lofiversion/index.php/t3130.html
In summary, the information I found was that the specific warranty I was purchasing only had a few advantages over the regular toyota warranty. They were a replacement car, dislocation service (if your car breaks down and you are 150 miles from home, they will pay for hotel) and the fact that this warranty would last for 5 years, where the toyota warranty is only 3 years or 36000 miles. This site indicates that you can buy an extended warranty if you want one before you hit the 36000 k mark, so I figure I can always buy one later.
I just drove back to the dealer and they are changing my contract to pull the extended warranty off. The last remaining thing which I am not sure of is that the sales guy indicated that buying an extended warranty later would be much more expensive than buying it when the car is new. Info on priuschat.com seemed to contradict this. Also, it seemed like that wouldnt make sense since i would be effectively paying for a warranty that just duplicates the one that comes with the car for the first 3 years.
One thing I did buy which I believe will be worth it is a fabric protection treatment and a rust proof treatment. I have read often on this site about the light colored interiror of the Prius, so I think this will be worth it.