Just for fun, I took a look at the search for "gas" at Google, MSN and Yahoo to compare the top listings for natural results as well as sponsored results. It was an interesting experiment which revealed what each search engine's expectations were of the searcher's intent.

It's important to pay attention to the natural search listings when you are planning your PPC campaign. This will give you an idea of what kinds of competition you're up against in the natural listings. It may be a good idea to place ads that are complimentary to those in the natural results.

Case in point, for the Google search results, most of them are showing sites about gas as in petroleum. The AdWords advertisers have got it right, since all the ads are related to gas as in the kind that comes from your stomach. Think about it, if someone is really looking for a solution to flatulence, they aren't going to find it in the natural results, so the sponsored results will look more enticing.