John's take on the role of brand in paid search in his monthly newsletter is spot-on:
If you examine the keyword searches that result in customers coming to your website, you will find that frequently the name of your company accounts for over half. I suggest that most of those who arrived via your catalog name did so as the result of a catalog mailing or as the result of years of brand development in the marketplace resulting from catalog mailings. In fact, when we track the curve of these clicks, we find that it very often matches the catalog response curve.
We write frequently about the role of brand and non-brand terms in a paid search portfolio; this is an critical issue for online marketers.
Winning at search involves growing sales cost-efficiently from both your brand and non-brand PPC keyword portfolios. Place extra emphasis on non-brand, as that's where you have your chance to meet new buyers.