I don't really see the need for adjusting/removing inactive accounts at the moment.
I don't think there are enough usernames that others may want to use to justify the work Chris would have to do to a) initially code it and enact it, and pi**ing around with the forum everytime we updated the software.
If we were up at 20,000 members then maybe this would be worth a look and the hassle.....but if we were up at 20k we'd have a larger admin team and more available time to do it