That's the best forum for all BMW's. 1 series, 3 series, etc..
Very up to date. The head people from that forum get invited to bmw screening events and they post up the info right away! Example of this was the reveal of the new BMW M4 at Pebble Beach. Guys from that forum literally had all the M4 pictures (100+) BEFORE the actual reveal.
I have a M3 and it is by far the best forum. Lots and lots of sponsor members on there and it is very very active.
Guess these guys get paid since they probably charge a whole lot to be a sponsor on that site.
One thing that is better than their site is if you are researching or planning on doing an European Delivery.
I used that forum to plan my itinerary when I did a European Delivery on my 2011 M3. Lots and lots of information about European Delivery planning. There is also a very useful wiki about European Delivery.