If I disable PPP from its admin page (i.e., from my profile page) the value of "Used passwords" field comes back to zero.
This is OK if I change the Secret, but I don't think so if I temporarily disable PPP (when I say "disable" I do not mean deactivating the plugin).
Consider also the case if I have used a lot of passwords and have striked them out on my printed pad: I have to re-print it! :D
Aldo
P.S.
Thanks for your patience: I am hardly testing this plugin because it's very very useful. ;)
http://wordpress.org/extend/plugins/perfect-paper-passwords/