From the Google Blog, in response to raised eyebrows regarding the 2006 Google Zeitgeist:

The Zeitgeist is “the spirit of time.” This is why when we come up with the lists of top searches on Google.com for 2006, we do not simply retrieve the most frequently-searched terms for the period — the truth is, they don’t change that much from year to year. This list would be predominated by very generic searches, such as “ebay”, “dictionary”, “yellow pages,” “games,” “maps” — and of course, a number of X-rated keywords. These are constants, and although unquestionably popular, we don’t think they actually define the Zeitgeist.

Basically, Zeitgeist is Google’s take on what’s hot, but not necessarily most searched for. To make sure everyone gets it, Google have updated the Zeitgeist page with new wording.

Related posts:

1. Paris Hilton and bebo top Google searches of 2006
2. How Google could bring RSS Mainstream
3. Yahoo! beats Google in customer satisfaction survey
4. Digging into the Year that Was, Yahoo’s Year In Review 2009
5. Sorry Google, Evo 4G Is No iPhone Killer (Android)