From the webpage:
AnalyzeWords helps reveal your personality by looking at how you use words. It is based on good scientific research connecting word use to who people are. So go to town – enter your Twitter name or the handles of friends, lovers, or Hollywood celebrities to learn about their emotions, social styles, and the ways they think.
Even though “…based on good scientific research…” I would not take the results too seriously.
Any more that I would take advice from a book called: “I’m OK, Your’re OK.” (I know the first isn’t likely and the second is untrue.) 😉
Play with it over a couple of days and try to guess the relationships between words and your ratings.
I first saw this in a tweet by Alyona Medelyan.