MySpace and Orkut both had over 100M users and failed, but it was because of neglect by their corporate owners, not a failure to monetize. AOL made it to about 30M at their peak; they're down to about 2M now.

I agree with the general point of this thread (that once you get to 100M+ users, there will be a way to monetize), but if you're trying to make the stronger point that once a company gets to 100M+ users they're invulnerable, there are ample counterexamples.

[1] http://mashable.com/2009/04/16/one-million-ning-networks/

Having "100+ million users" is a relatively new concept, period. It shouldn't be surprising that very few, if any, have failed. But that doesn't tell us anything about the future.

Before Enron, how many companies with $100+ billion in revenues went bankrupt?