We have implemented this and just like to say its working well for us.  Would recommend to others for added security due to the one-way encryption.
DB field:  set to varchar(255) - this should help others.
Other general users report it to be 123 chars, but on on some of the PHP documentation is states: 
"255 characters would be a good choice" - I second that. 
PHP developers: GOOD job btw!
