I lurk on MBB. Prior to The Great TERB Crash (3 - 4 years ago?) TERB & MBB were pretty much equal in terms of traffic. After The Crash it seemed that about half of the main TERB crowd stayed on MBB and the other half came back here. For a while, it was quite common to post a review on one board then copy & paste it on the other one.
But I think TERB was and still is easier to find. For casual surfers, I think Google, yahoo etc may direct people here first. The creation of The Lounge also helped to precipitate a lot more traffic here as people started posting about anything and everything. MBB on the other hand has, I find, tended to stick closer to the reviews and less to the general discussions. On the whole, this give MBB something less of a community feel which to me, is what makes TERB special.