My iPhone and IPad don't have Spambayes. So, while my desktop is spam free thanks to Spambayes, my iDevices accessing the same email accounts are plagued with spam. If all ham were emailed to another account, and that account was unknown to the rest of the world (i.e. no spam) then the iDevices could access just that account and get pure ham.
So how about adding an option to the "Certain good" section that allows forwarding to another address?