I've been setting up Google Adwords campaigns for therapists for over 2 years now. In the last couple of months, I've had some people come back and say "hey, my ads aren't working like they once were." And it's true. Google has made the whole Adwords business a lot more complex - and the main cause is an innocuous phrase - Quality Score.
Back in the old days, where your ad showed up was based on only two things: your bid ($) and how often your ad got clicked (click-thru-rate, or CTR). But during 2008 Google started adding in more and more criteria for whether your ad showed, how high it showed, and what the minimum bid was. For some people, they found that their minimum bid had gone from 25 cents to $5 or $10! (That's what is known in the biz as a "Google Slap").
Google is as mysterious as the Wizard of Oz, so while they do point and describe some of the things that go into Quality Score, they never come out and tell you exactly what it is based on. So, as usual, cottage industries have been born to figure it out and read the tea-leaves. It's really quite similar to SEO.
That said, dear reader, do not panic. This is all based on relevancy (as seen by Google's computer). If your ads are relevant to the search, and the site is relevant to the ads, then it'll all work fine. But there are times when it goes haywire.
The hardest times for me have been telling people who just invested in a gorgeous Flash-based site, or a frames-based site, that Adwords was going to be a nightmare for them, because the spiders couldn't see their content. Then there is the issue of getting out of a hole, because Google includes your history as part of the Quality Score.
This is not meant to dissuade you from pursuing Adwords, I still think it's the best mechanism I know for marketing. It is meant to explain the growing complexity of it, and why what you did in 2006 and 2007 might not work as we enter 2009.
But if you need a consultant, I know this one guy....... :-)
Your Google Guy - Web Marketing for Therapists