I handle pay per click campaigns for most of my customers. The front-end, setting up and tuning the campaign is the most time consuming part of the effort. Finding the right words and then determining which words best convert. After the initial set-up maintenance requires far fewer hours, with much of the time spent adjusting spend for postion. However diligence and attention are important as results should be fed back into the website to improve landing pages and improve organic results for top performing phrases.

It is interesting to see how people charge for this service (most of my clients are hourly). There is an excellent article about PPC management options here