From Kevin Kelly's blog:
...the actual number may vary depending on the media. Maybe it is 500 True Fans for a painter and 5,000 True Fans for a videomaker. The numbers must surely vary around the world. But in fact the actual number is not critical, because it cannot be determined except by attempting it. Once you are in that mode, the actual number will become evident. That will be the True Fan number that works for you. My formula may be off by an order of magnitude, but even so, its far less than a million.
I've been scouring the literature for any references to the True Fan number. Suck.com co-founder Carl Steadman had theory about microcelebrities. By his count, a microcelebrity was someone famous to 1,500 people. So those fifteen hundred would rave about you. As quoted by Danny O'Brien, "One person in every town in Britain likes your dumb online comic. That's enough to keep you in beers (or T-shirt sales) all year."
Others call this microcelebrity support micro-patronage, or distributed patronage.