The dip in frequency of passwords with 7 characters is pretty interesting. I was curious so I checked the frequency of words in /usr/share/dict/words as a function of their length (http://chart.apis.google.com/chart?chxl=0:|1|2|3|4|5|6|7|8|9...). There's no such behavior in dictionary words as you can see. We can however see that in both passwords and words that the frequency of length 7 is about 80% of length 8 though. My first guess would be that length 6 gets a boost in the password data because a large number of people think a password shorter than that is too insecure. Only 36% of the passwords were dictionary words but it's still fun to guess about.