Just listened to a Texas Realtor pod about password security. It said that adding just one character to a password will greatly increase your password security - for instance, between letters, use a sign or symbol such as an @, #, &, etc.!
Also, it was suggested to make your password eight characters instead of seven when possible, as well as using upper and lower case letters plus numbers, not just all lower case letters.
Using all lower case letters could take a hacker approx. 2.25 hours to figure out, versus possibly well over a year (and much, much longer) if the above tips are used.