[kh99]

You could make new columns in the user table to save one or more ips, then fill them in whenever someone posts (like keep the last 5 ips posted from or something like that). Then you could do a one-time processing step to fill them in with past posts, or just forget that and start filling them in for new posts.

You'd still have to search all users for matching ips for a postbit (or in the profile), so you'd probably need some kind of an index on the ip address cols for that, and I'm not sure what effect that would have.