I have been using AdWords for almost 1 yera and has seen a high rate of as good as 17%. This is not because I have good copywriting skill, but because of the excellented keyword selection (a horse or horses tipped as worth bets in a race or meeting) facilities (a building, service, or piece of equipment provided for a particular purpose) inside the AdWords system. The success on AdWords is largely dependent (relying on someone or something for financial or other support) on keyword selection. Tool such as overture, Wordtracker are a big help for marketer.