I do AdWords for a customer website and he finds them to be a cheap and efficient way to advertise.

One thing I've found helpful is to create a dedicated "entry page" for visitors who go to the site via Google. You can create several sites (one for each AdWords campaign you're running) and provide the different customer groups the info / advantages they want on the first page they see. This way the surfer will most likely stay on your site and explore it further.