Resolved. .htaccess file edit from an add-on was interfering with this modification.
Uninstalled their mod and kept this one.
Thank you for all your contributions to vBulletin, modifications and otherwise.

This was disabled by the upgrade to vB 4.2 on a test board (I'm guessing because of the Members who have visited today modification's inclusion in 4.2), but I can't find the equivalent functionality within 4.2. Would I be correct in assuming that it's not in there? If so, are there any plans on a 4.2 modification? I'd hate to lose this since it's quite useful.

Yes, there will be a 4.2 version.

I can't get this to work in 4.2.0. For starter there are no hook forumhome_whovisited_list anywhere in templates

Edit. I did not realize that Visiting Members options had also to be set, in addition to Members Tracking options.
is there a way to restrict Visiting Members display to display members tracking?

edit again. Never mind. I put a conditional to restrict that

I dont understand what you mean.

Never mind. Members Tracking works only if Visiting Members is active and I did not want to display Visiting Members to certain groups, so I just put a conditional in there.

I still dont understand. Tracking does not need Visiting Members to be active, it has its on on/off and permission settings.

Depending on permissions, you can have ;

1. Groups that dont see Visiting Members at all.
2. Groups that have the Visiting Members Display, but no access to the Tracking functions.
3. Groups that have the Visiting Members Display, and access to the Tracking functions
4. Groups that dont the Visiting Members Display, but do have access to the Tracking functions.

Option 4 would be unusual as they would need to manually type in the urls for Tracking displays.

It does as it uses in template FORUMHOME as an if condition. And that is true in forum.php when
if ($vbulletin->options['wgo_members'].

I spent a couple of hours trying to figure it out. When I saw that in template I turned it on and ... it started to display.

here is the mention of it in template

Right, now I see what you are getting at.

In 4.2, this hooks into the existing VM display, it does not add its own, so yes, it obviously needs the master setting to be turned on, otherwise no one will be able to see it.

That still doesnt explain what you said, or why you would add a conditional anywhere.

You do realise that Visiting Members Display is controlled by Usergroup Permission ?

So while the Master may be on, it only displays for usergroups that have that permission.