Can anyone recommend a good book or site about using adwords and how to customize/optimize the ads?

I've read Mastering Google AdWords. Don't know if it's better than others, as I bought it just because it's the most popular :) eBook claims to lower advertising costs, however, I haven't found time to optimize my ads yet, so can't tell you if it's true. I'm sure all the information might also be found for free with some research on google.

There is plenty of information available is you take a look. To be honest once you spend a bit of time within the Adwords tool you soon learn the tricks of the trade and how to get the most from your money.