[SNIP] I doubt
there are many people with accounts with the same
password but different email address, so the gain is minimal. [SNIP]
There are a lot of people, like myself, who have started using different
e-mails for every site they sign up to. For example,
wikipedia_aug07(a)example.com would be the e-mail address I would use if I
joined WP today.
Maybe there are also a lot of people having beside different email
adresses also different passwords(startings/endings) on each
account...