Recently, I had a user ask if it was possible to require that a password meet certain parameters. Specifically, his client wanted to require that passwords contained at least 2 uppercase characters, 2 lowercase, 2 numbers, and 2 special characters. Lastly, the password must be at least 8 characters long. Working together, we were able to come up with a little customization that would not only suit the clients requirements, but also would require minimal effort to maintain.
A primary consideration when customizing this (or any) plugin is how hard will it be to upgrade the plugin. WP-Members has a number of features to make this process more flexible. Much like WP itself, WP-Members uses filter and action hooks which allows you to upgrade the plugin without overriding your customization.