One of the issues with Password Strength is:
Generally, they are not secure and hard for users to work with and understand. As an example:
Which of the following two passwords is stronger, more secure, and more difficult to crack?
D0g.....................or
PrXyc.N(n4k77#L!eVdAfp9
You probably know this is a trick question, but the answer is: Despite the fact that the first password is HUGELY easier to use and more memorable, it is also the stronger of the two!
In fact, since it is one character longer and contains uppercase, lowercase, a number and special characters, that first password would take an attacker approximately 95 times longer to find by searching than the second impossible-to-remember-or-type password!
Passwords that are too weak of course invite brute-force attacks. However, we find that relatively weak passwords, about 20 bits or so, are sufficient to make brute-force attacks on a single account unrealistic so long as a "three strikes" type rule is in place. Above that minimum it appears that increasing password strength does little to address any real threat. If a larger credential space is needed it appears better to increase the strength of the userID's rather than the passwords. For large institutions this is just as effective in deterring bulk guessing attacks and is a great deal better for users. For small institutions there appears little reason to require strong passwords for online accounts.