Hi Jon. :) From what I understand, the database query to generate those names is quite resource intensive, and in MySQL, includes a LEFT JOIN, which tends to increase the resource usage even more. I was reading about users with large vBulletin installations over at the Admin Zone forums, and a few of them with large vB forums disabled features like this one.

I did notice when I turned it off completely on the forum home page, the page loaded faster than I've ever seen it. (You can set this under Forum Home Page Options --> Display Logged In Users, with options for No, Yes (random) and Yes (alphabetical). Heck, even if we could find the code that makes this setting conditional per usergroup, it might be a start.