I have today been playing around with the Google insights website, which lets you see the trends for keywords that you put in.

http://www.google.com/insights/search/

Here is google’s post on it http://googleresearch.blogspot.com/2009/08/on-predictability-of-search-trends.html

One of the statements from the research is that over half of the most popular terms were found predictable in a 12 forcast. There are also more predictable categories such as health, food and drink and travel. The least pradicatble categories are for the more rapidaly changing entertainment and online communities and social networks. So I guess they cannot predict who will be the next facebook yet.

A good way to use this tool is to look at how search trends change, an example is the terms, Buy movies online and Buy DVD online which cross as people become to consume movies by different methods.