As far as I undrstand it (and please correct me where i'm wrong):
Ayu-youkou - on the main forum page (in the bottom half) you should see a box with 'currently active users' underlined above it. That will show you who is 'active' (minus those users who have chosen to keep their online status hidden).
If you actually click on the 'currently active users' link, you get that message, because the true list of
everyone who's online is only available to members with special privileges - 'Donators' for example.
I would guess that the other times you've seen that message, you've also been trying to click on areas that are reserved for admins/moderators/etc.
Uncle Frank - many thanks for your explanation
As Ayu-youkou said, the other thread left it a bit unclear about the use of IP tracking, and the reasons for it. I might be travelling a fair bit around the world this year, and accessing the forum from different countries, so that was certainly a concern for me. Your post has certainly greatly reassured, but at the same time it would be nice to hear if other folks in the 'empowered' positions here do any more than that with IPs, for security and privacy issues alone...
cheers!