Many big brands and small brands do it, even if they rank in the first organic spot for their name. I did a search on Crate and Barrel (which my finance is obsessed with) and you see the PPC ad, I am not sure if it is an affiliate ad or an ad by Crate & Barrel themselves, but I believe it is an ad paid for by Crate & Barrel. Heck, I even bid on my own brand name on both Google AdWords and on Yahoo! Search Marketing. Why do I do this?
(1) Other companies were bidding on my name, and I wanted to be the first, not only on organic side but also on the PPC side. (2) It builds up brand recognition, even for a small brand. (3) Its targeted traffic and conversion is likely. (4) It cost next to nothing for my brand.
Forum discussion at WebmasterWorld.
