The NYTimes is running a good article called, "Real Life Lessons in Using Google Adwords." It seems that for every person I meet who loves Adwords, I can find another person who feels like they are a rip off.
Google Adwords are a form of pay-per-click advertising which means you only pay if someone clicks on the ad. While this seems like a great system (and generally is) you can find your ad bills stacking up quickly if you don't properly target your ads. If your ads are showing to too broad and audience you will probably pay for a lot of clicks of people who really aren't that interested in what your selling. On the flip side, if your ads are too targeted you might not get anyone clicking on the ads.
My experience from running Adwords for KTG is that success comes by figuring out two important things:
1. Targeting Ads for the correct search terms. This is a balancing act between too general of an audience and too specific and audience. To do this properly it takes time and work to analyze the performance of your ads.
2. Getting the person who clicked the ad to say on your site and contact you. It's important that after you paid for someone to click your ad you don't loose them. This again takes looking at the analytics data and trying to figure out how to keep the visitors on your site and getting them to contact you.
But don't take my word on using Google Adwords, read what the experts have to say.