as an admin for a number of sites I have a whole bunch of forwards that eventually make their way (usually via a specific upstream address so I can quick redirect them) to my SpamCop address which is my main line of defence against drowning in spam....
I'd love to start using the MailHosts (especially as it's running the risk of actually becoming mandatory one day) but... the risk factor is a bit high !
Would love to see a totally automated solution for adding mailhosts, but, yeah... right.... computers can't deduce the right answer to this question, so... perhaps a check list that's been monitoring hosts and if you manually (via webmail as well) report one as spam it gets dropped, but you can also go into the list and manually select which ones are good for you.
I get a little nervous about making something like this mandatory without a low pain adoption route....