Shannon wrote:
But isn't the purpose of a Trademark to keep someone from stealing a source identifier? Finding a competitors advertisement in a search for a trademarked company does not confuse who the source of the trademark is.

The reason that you want to keep someone from stealing a source identifier is so that person cannot fraudulently profit from the name recognition, branding, and advertising done by the real source. For example, you've heard of the "yellow pages" and you go looking for the "yellow pages" and you pick up the "yell-o pages" instead. The proprieter of the "yell-o pages" is profiting from the advertising that the "yellow pages" is doing. Purchasing advertisements on someone else's name does precisely the same thing. The first person spends money building their brand, and you get to reap some of the benefit from piggybacking on their name recognition.

RE: Google's broken Trademark precident