I concentrate on cost per conversion - its important to have a CTR of better than 1% so that adwords knows that your ad is relevant but the real deal is understanding the cost per conversion. To misquote Dickens: Adwords cost < total cost per conversion, result = happiness Adwords cost > total cost per conversion, result = misery
for 1 of my adwords campaign I am getting a CTR of 35-40%, that all due to strategic placement of ad on specific websites only.