We have a quasi internal/external community since the users are all known members but they work at separate organizations throughout Canada. We use email marketing to promote use of The Airport Link, which is how we have branded Clearspace. We welcome each new member with an email about the system. Then we also have periodic "Link Tips" which remind people about how to use the system.
We started off our "marketing" efforts as casually mentioning it to folks we knew were passionate about E 2.0 solutions who we knew would go and share it with their friends...you might call it viral marketing.
That has largely remained our marketing tactic, although we have begun to actively promote EMC|ONE a bit more these days...
We have integrated a live RSS feed of the 5 most recent discussions on our company intranet site, so folks that go there for information on all sorts of things will be immediately presented with the recent goings-on, as well. That has resulted in a ton of new interest.
We have also written up a couple of news stories in our internal publications, but those have not been as successful as the live feed.
We're also actively reaching out to and presenting the solution and value to groups across the enterprise, which has been very successful, as well.
Our run rate is pretty steady at about 200 new users per week, with some fluctuations as we on-board new key groups.