Have you ever needed to Google for something? You might have even heard someone say they "Googled" something, when they were actually using Yahoo! search. As silly as it sounds, Google has become so popular in modern culture that it has made it's way into Merriam-Webster's Collegiate Dictionary.
To some this may sound like some excellent free advertising, but as companies like Xerox and Kleenex have found out, having a brand name in the dictionary isn't the kind of exposure you might always want.