In our 4 years ScubaBoard has rarely done any direct advertising (ppcs, banners, magazine ads), however, we do a lot of indirect promotion using stickers, tshirts, banners at events and anything else that will build word of mouth. This has worked well enough and brought us to about 1,000,000 posts. Still, the bigger you get the more you seem to do to keep the growth rate increasing. Word of mouth, inbound links and search engine links keep us growing nicely but we have begun (or I should say, re-activated) some ppc and print ad campaigns. Right now we are spending a few dollars here and there for ppc terms but it's very specific stuff and not really high bidding. The goal os any campaign for a community should be to target those people who will join and participate as best possible. For example, if you run a forum like DaniWeb's which covers hosting advertising for the term "web hosting" would probably not be an ideal use of money, especially if you compete for a top spot. The more specific the term and the more informative your ad is, the more likely you will be to attract people who want a forum. Remember, the goal is quality... quantity means nothing if you have a 0.01% sign up rate (unless the advertising is dirt cheap). Don't forget to count stickers, shirts, cds or anything else you can use to brand your name as part of your advertising campaign. Many sites forget the power of word of mouth yet word of mouth is what makes most sites what they are. The more you can feed off of what you have the better your campaign will be -- it is always easier to have your users help promote you (even if they don't realize it) than try to "cold call" new users.