In our forum we create a kind of game: Masters and Students. Every Master must have two "students" until they become Masters themselves. The system creates a interesting sense of "family"

That sounds like an interesting concept, Deriel.

Does that start with staff or just a member thing?

Are they listed as such in their postbit or anywhere else after they attain the "Master" rank?

We made some simple rules and invited some of the best (and older) users to became the "first generation". After that it's almost automatic.

We use an algorithm - not perfect, but sufficient - to give grades from A to F to the students (we call them "Nolyoni" - students in Quenya, one of the languages created by J. R. R. Tolkien) in a bi-weekly basis. The promotion to master ("Saitor", also in Quenya) is after some weeks obtaining good grades. There is a custom userfield in the postbit that shows the rank.

And better: all the users try to make good posts, to receive a good grade =]

just keep posting, participating.

You won't keep the sense of intimacy as your board grows bigger, that's unavoidable, but you should let your visitors and members know you're still there. Be sure to keep involved in micromanagement: moderation, conflict negotiation, newbies doubts.

You can't avoid losing the sense of intimacy, but you still can demonstrate your users you still care.