I followed the same route:

Starting with Adwords on 2003 it aligned well with my business as a complement to SEO. I could test different keywords and it worked. Nobody beats AdWords at the audience and self service system.

But then, we started to see keywords at $ 2, $ 5, $ 10 ... wow, for just one click! At the end we stopped all our campaigns and spend our promotional resources to our blog. And our blog, scientifically, have a better ROI.

I would add that now AdWords is more difficult to administrate than Windows Advanced Server with Exchange.