(Reading hint: If you’re already familiar with the value of negative keywords in PPC advertising, skip to my last paragraph for my new suggestion.)
Your mother and your favorite motivational coach will both tell you: negativity is a bad thing. However, when it comes to pay-per-click advertising, going negative can be a very good thing.

I’m speaking, of course, of so-called “negative keywords,” keywords that you don’t want your pay-per-click ad to show for. Negative keywords are perhaps one of the most overlooked–and yet most useful–ways of improving the performance of your ad campaigns. Why would you not want your ad to show? Isn’t any exposure good exposure?

In the “old days,” maximizing exposure was certainly the highest goal. When you’re advertising in print or broadcast media (TV, radio), you’re throwing spaghetti at the wall and hoping some will stick. You can’t micro-target your audience in those media, so your best hope is to expose your message as many times as possible, counting on the likelihood that some of those times potential customers will see it.

But one of the great advantages search-based advertising gives us (arguably its greatest advantage) is the micro-targeting that older forms could not offer. With finely-tuned keywords and ad text, an advertiser can have real hope to get his message in front of actual potential customers nearly each and every time it shows. Conversely, a PPC advertiser will want to have his/her ad not show to potential clickers she/he doesn’t want or need.

This is where negative keywords come into play. Say that you are marketing iPhone apps, but all the apps you’re marketing are pay apps. You should include the negative keyword “-free” in your ad campaigns because it is highly unlikely that anyone actively searching for “free iPhone apps” will convert on your pay-only app site.

Now here’s my suggestion to the folks at Google AdWords: Create a report in the new AdWords interface that displays the potential top negative keywords for any ad group. This shouldn’t be hard to do. The new interface already has an awesome report that displays the top actual search phrases that triggered a group’s keywords (very useful for discovering valuable phrase and exact matches you should be targeting). The only bad thing about that report is that it only displays phrases that actually resulted in clicks. Now that can still be a good source of potential negatives. But what would also be useful to know are the phrases that are generating lots of impressions for a keyword but no clicks. Those are CTR and Quality Score killers. So basically, the report I’m proposing would display the phrases that generated the most impressions with zero clicks, in descending order of impressions. That seems to me like a gold mine for some very positive negatives.