I have taken a chainsaw to the wiki users list; while we had antispam protection preventing new users from creating pages it wasn't stopping them creating pages and we were up to over 80,000 accounts. I started trying to sensibly weed these out, but it's hard to distinguish. So I resorted back to cruder methods, making sure all the accounts listed on:
http://www.alug.org.uk/MembersGroup
existed and trying to find a handful of users I knew should be there but weren't. We're now down to 14 users.
If I have inadvertently culled your account let me know and I can bring it back from the dead (and ensure it gets added to the MembersGroup page).
J.