Much of this article states a few obvious facts about ROI. Once you get through it, the rest talks about taking you search campaign to a higher ROI. Many of the companies I meet with make the mistake of summarizing the results of their campaign. In other words, if their entire campaign has a positive ROI, that is good enough. Few companies really work hard at finding an optimal ROI for each specific keyword.
Portfolio PPC Campaign Management, Part 2:
"Failure to achieve optimal profit levels is portfolio-style campaign management's greatest risk. Unfortunately, too many agencies, internal campaign managers, even search engine reps don't understand the best portfolio has each keyword listing at its optimal ROI all the time. Campaign managers unaware of best practices often allow some keywords to cross into negative profit. Ouch! To add insult to injury, performance reports hide the negative profit in a successful average ROI metric. If you can't see the individual results of a campaign at the most granular level, you'll never know the real deal.
Another common failure occurs when you use the same short-term ROI metric (CPO, CPA, or ROAS) for the entire campaign to simplify it. Don't oversimplify your business."