The tool, developed by two researchers at New York University, sends random searches, such as "boston clock" and "croissant," to the four largest search engines [ .. ] A fake search is made every 12 seconds under default configurations; the tool can generate millions of unique queries from its list, and users can add their own.
If you are interested in the plugin itself, you can visit TrackMeNot's website. They make no bones about why they made the plugin:
We are disturbed by the idea that search inquiries are systematically monitored and stored by corporations like AOL, Yahoo!, Google, etc. and may even be available to third parties. Because the Web has grown into such a crucial repository of information and our search behaviors profoundly reflect who we are, what we care about, and how we live our lives, there is reason to feel they should be off-limits to arbitrary surveillance.
While many people don't care, a lot do. Enough that this plugin may actually become quite popular. I wonder what the search companies would feel about a plugin like this, assuming it ever was used en masse.