I host a general-interest VBulletin forum, which at one point had something like a hundred people posting. One day, we discovered that via the "groups" functionality, there was a whole
parasitic forum co-existing with ours - we didn't know it existed, we didn't know any of the people there, and they didn't know us, and the two groups didn't interact
at all.
I wonder if it's possible for something similar to happen on specific-interest a messaging board, but just as a function of time zones. (e.g., somehow, most of the population of the board is from Spain and New Zealand, 12 hours apart.)