What Murray mentioned about small numbers reminds me of the Dunbar number of 150 persons. Robin Dunbar noticed that groups were more stable around this number. Schools (for example) functioned better when of this size or divided into sub-groups of this size (often called houses) The Gore-Tex factories have 150-200 workers and when they need to expand they just build another factory next door or a few doors down.
I don't know how this would play out on internet forums though. Perhaps up to 150 or so daily active members, but this would have to be self emergent, not regulated. (God forbid that.) The only time I've really noticed too many members was years back on a Harry Potter forum. That site was crazy!

In half an hour your question could be on the second or third page as there was so many new posters. I suppose it was like fly fishing. If you didn't get a bite immediately, you weren't going to get one at all!