Mastodon itself is interesting technology. Rather than a central, single instance like we have with Pnut/10C, anyone can set up their own instance of it. Those instances can operate under the own rules.
What sets Mastodon apart: Federation. Federation allows you to follow people on another instance. Likewise, people can follow me on the various instances I'm on.
It's kinda like email in how people can reach you and that you can have multiple identities.
This gives you the benefits of a small community like we have with Pnut/10C with the global reach of a larger network, thanks to all the instances. Further, if one instance folds, or the one you're on sucks for some reason, join another.
The fact that the Twitters, Facebooks, and Googles of the world will have a difficult time monetizing or controlling the network is a feature, not a bug.