I've taken a slightly different approach which I hope will help as I think (not sure) but quantity is involved in weighing 'spam', and handling mailings to users.
Each quarter, I add a new group like 2002Q1, 2002Q2, and throw the switch for the default group on or about the time the quarters change. Now I can divide up batches of outgoing with ease and also get to see and query the site growth progress right away. I check the bounces every day or two and simply remove the users subscriptions. If the user has a distant last on date, they're history. Certainly the entire users group could be queried by date to produce similar results, but this is just too easy.
Seems to work pretty well.
www.UtterAccess.comGord Hubbell
