Over 600 social networks and counting!

In my search on social networks I have never found a figure stating the exact number of networks which are around. Logical I hear you say: every day there is a new social network that sees the light and another that's being sold to a large corporation. The times that I have found estimated guesses they usually ranged in between 200 and 400 networks. As I am slowly finishing up my book on social networks, I can now say for sure that there are over 600 social networks out there as we speak (yes , over 600!).
It took me a while to digest this information -and an even longer while writing about them all :-) -but there you go.

In the mean time please continue sending me information on social networks which might have escaped my attention- if there is room for 600 why not make it 601?

ps I checked: there are no social networks in Zanzibar (where I spent my holiday the last two weeks).