For Google, Adwords is their big revenue generator. So not surprisingly they work hard to make it successful for Adwords publishers. They provide a wealth of information, some of which can be found at the Google Adwords Learning Center.
The better the quality of Adwords ads, the more readers will appreciate them. In turn this will improve the readership of ads, which is of benefit to Adwords publishers. This continuing improvement spiral is win/win for all. It was for this reason that last year Google introduced the quality index for Adwords ads. This considers both the ad itself and the landing page from it.
The latest innovation is to give advertisers reports on their Impression Share. The Inside Adwords blog gives more information on this:
“Share of voice” is a metric often used in the advertising industry to represent the relative portion of ad inventory available to a single advertiser within a defined market over a specified time period. Impression Share, a new AdWords metric, is similar to share of voice — it represents the percentage of times your ads were actually shown in relation to the total number of chances your ads could have been shown, based on your keyword and campaign settings.
Not every advertiser’s goal is to appear each time his or her ads have the opportunity to show; however, Impression Share is a convenient way to assess shifts in the competitive landscape as well as ways to diagnose where you’re losing Impression Share.
In total, the support available to advertisers is impressive. When coupled with the ability to measure conversions using Google Analytics, the ability to assess performance is beyond that available in any other medium.