This article tends to give some answers to that question. I found it both interesting and disturbing at the same time. It seems that growing from 25-35 to the next plateaux of stability, around 80, is full of dangers and difficulties; and the next one will come only with 350-500 people!
This actually is present on SL's group structure as well, as regarding land. Getting one sim full of people (ie. around 25-35) seems to be "easy" when you go beyond the 12 people barrier. Getting a second/third sim (ie. 80 people total) is also quite stable; we see many 3-sim-communities spread around in SL: Ginko, Ravenglass Rentals, etc. But the next plateaux comes with about 10 sims. Anshe's success seems, according to this theory, to be predicted by her successfully surpassing the 10-sim-limit barrier.
Well, I'm still struggling with these ideas and thoughts, and will host a meeting later today at Thinker's, if you care to discuss it

