Having just joined and reviewed the terrain, I can see that they have three advantages to us:
1) No age limit
2) A forum specifically for gossiping about the stuff on other boards... oh, that is sweet! Can we have one of those here?
3) Very funny registration agreement terms... although I can't remember what the one here says, maybe ours is funny too.
However, on the downside, they have no link at the top of each thread page to return to the forum in which the thread exists. Confusing!