I've seen sites running phpbb with 1000's of posts per day. The big issue is whether the server can handle it. A site like that requires a dedicated server, currently the plan i have now has a lot of resources left. At least double what it's doing now. I've been flirting with the idea of renting a server, I have a ready made list of customers already to share it with... I'd about break even.
Trouble is Server Admin is not a hat I'm confident I can wear yet....
Well, I'm off to reading the Apache manual.
It's all about getting the word out from what I hear
That's part of it, inbound links from other sites are important but that's not even the half of it... actually not even a 1/4 of it. I won't give the farm away but just as example a standard phpbb forum ios horrendous for a search engine to try and index, the standard install has at least 5 or 6 different URL's that will all go to the same exact content. This is not good, the search engines won't index you as much nor will they place much relevance on your pages because of the duplicate content. This forum however has only one URL per unique page that Google will find. That's one of the changes I made way back in April and I still have a couple of thousand duplicate pages inGoogles Index that haven't been removed.Slowly but surely they are being removed and the duplicate content penalty for a lot of pages is going away and they'll show up in the SERP's.
FYI, phpbb is easy to install as long as you can read directions. It only requires PHP and MySQL which is common on just about any hosting plan.
Having done it many times i could have a inastallation up and running in about 5 minutes.