I'm in awe of how busy this forum is compared to many other sites that have forums in this niche that started around the same time. One thing I can see is that Digital Point is using a out of the box version of vB, very nice. I personally don't like heavily modified forums. Also there is not over advertising. Why has this forum grown so fast to get to busy?
Yes, DP is a great forum. But I am not sure if its really using a modified version of vb as I have seen such modifications on other forums as well. The reason it has grown so fast is because everyone can gain a lot of knowledge here on various topics and the members are really nice and don't flame each other. Plus, the marketplace is free.
It only looks that way... There are currently 173 custom plug-ins that alter how the forum works (most are individually small improvements from a stock vBulletin). I'm not personally a big fan of changing something for sake of changing it (like a complete reskinning). I'm more in favor of improving on the specific things that can be improved on.
The strength of DP is its members who are all very keen to help others - even Dumbo's like me who are totally computer illiterate. That's why people keep coming back. Davmac