www.TheRarestWords.com - try this to see what words other websites are using and how it's compared to you. You can add your own URL (or remove it if you want). Check also this article in Techcrunch too: http://www.techcrunch.com/2008/05/23/therarestwords-intriguing-semantic-seo-project-from-russia/ Maybe you'll find it helpful....
Then read their blog: http://rarestblog.com/ If you still don't understand then maybe it's not for you...