fantanoice's Zetaboard forum (Dashing) got around 30,000 posts (from memory) before it got it's domain. It's nearly at 90,000 posts.
Bear in mind, that was after it was merged with my old Forumer forum (which had about 50,000, which is surprising because Forumer is an absolutely horrible host) when it moved to MyBB.
http://s1.zetaboards.com/dashing
http://dashing.forumer.com
^ For those were interested... (not advertising because they're no longer running).
There was also Brawl Domain, which was exceedingly popular for a Proboards forum. They too have moved to self hosting.
it's really content and to a lesser extent a nice theme that draws members. Word of mouth advertising to the right people is what you really need to get your forum off the ground initially.
^ This. You can start a forum on any software or host and have the potential to be successful. Frankly, I see self hosting as a good move for security and customisation reasons, but would never regard a self-hosted forum over a remotely-hosted forum for that reason along. Same with domains, they're great for image, but wouldn't regard a forum with a domain higher than one without based on that reason alone.
It's about 'community,' not software. Many people think that a successful forum is one with hundreds/thousands of members, thousands/millions of posts, they're own software/self hosted, domain and a bunch of other things. While this is awesome in it's own right, it's not exactly true. A successful forum is one that can hold it's own as a community, which was something that I always did at Dashing (and I suspect the same over at Brawl Domain and other sites). You need a functioning community to be a working forum.
It's like the mechanics in a video game. You can make a game as pretty as you like, but without working mechanics, it just crumbles.
If you have a functioning community, then you can succeed with any forum software or with any URL address.
Yea, it looks so unreal....But I guess they spend money on advertising instead of buying domains.
...lol, no. Usually when people don't have domains, they don't have the money or they don't know how to use it. Frankly, it's a lot easier to buy a domain than it is to pay for efficient marketing.