Quick example, though: of 6936 patterns currently in my list, if you just run a cut on \\ (which catches either '.' or '-' as the next char, for the most part) you get (matches of 20 or more):

count first left-hand pattern part ----- ---------------------------- 1572 ^[0-9]+ 206 ^.+ 200 ^host[0-9]+ 179 ^host

Exceedingly long list cut.... Just to throw in my own 2 cents: I find it really ironic that we rely on reverse DNS data that potentially comes from a spammer in order to determine whether or not someone is a spammer. It probably works for the zombies. But in the long run, ip based filtering is quicker, since there's no DNS check and you have a better idea of the size of the netblock you're filtering. I'll be a lot happier once the smtp-submission port (587) catches on. It will make filtering a lot simpler.