Jim Lanzone, over at the Ask Jeeves Blog, has an interesting entry which helps shed some light into search-engine revenue. In the past we've wondered how much revenue comes from top keywords. While some argue that the "long-tail" niche keywords are what drive search-engine revenue, it seems possible that searches for "mortgages" with their high cost-per-click, and their search-frequency in these times might account for an outsize chunk of revenues.
The entry doesn't get that detailed, but it does say that 70% of revenue comes from 30% of search keywords--an surprisingly (impressively?) short-tailish number. Since AskJeeves uses Google's Adwords, there's a fair chance that the ratio is similar for Google. Obviously, we need a lot more data, but it does seem that a search engine could be vulnerable in fluctuations to their "big sellers", much the same way a bookstore is dependent on Harry Potter and the latest incarnation of the carb-free diet.