<< It already does that for subscribers when a freeloader posts a link.
Russ, NCNE >>
Actually, my suggestion was slightly different I think, and it's complementary. I'm going to guess that for subscribers, the link is changed on the fly as the post is pulled from the database. This puts a little extra load on the server, but since the subscribers have their own box and there are relatively few subscribers, I can see the overhead being acceptable.
My suggestion is to change the links as the post is submitted to the database, thus it's a one-time change. It would effectively be a "physical" change to the data, and the processing overhead would be significantly lower.
To accomodate the subscribers wanting subscriber links, the dynamic replacement of "forums.anandtech.com" with subscribers.anandtech.com" can still happen as it apparently does now.