P.S.: Perry writes much better copy than I do, therefore, I save you from having to bear with me and urge you to go over to his site and read what he has to say about Google Adwords in 2009/2010 and why you need to get his book.
Actually you don't even need to read everything.
P.P.S.: Update April 19, 2011: I just discovered that Perry has updated his Definitive Guide To Google Adwords and calls it - Edition 2011.