Thank You Peter R! I will add this model to the toolkit when I try to explain to people why sometimes (2013) it rises 100x and sometimes (2012) hardly at all. Randomness.
Randomness is not the only possible explanation. Log-logistic adoption is another possibility for a declining rate of price appreciation given Peter R's model correlating adoption to market cap and given the market cap is growing.
So it is not sufficient to say, "the model must be my fit, and randomness explains why the fit is off this year".