Rand posted an update to a tool named keyword difficulty tool. The tool's name is pretty descriptive enough, it tells you how competitive a keyword is to rank for. There is great detail on how it works here and here.
I did a test on the term "seo blog" for no good reason. After waiting the specified amount of time, I was given a ton of details, which you can read in this pdf document (1.5MB) .
Save up to $400! Register now for SES New York 2012, the Leading Search & Social Marketing Event, taking place March 19-23. Google's Digital Marketing Evangelist Avinash Kaushik will keynote. Hurry, pre-agenda rate expires March 2!