What makes the community great?
One thing that I notice is how integrated it is - great topics are highlighted in the word-of-mouth blog, queries are moved from twitter to the forum (and vice versa, when looking for more input it's promoted to twitter). Tom's blog is woven in there, too. You don't feel that you *have* to go to the forum for help, support or ideas. I think much of that is down to the staff who really moderate and manage the community. It's a mix of organic/user-driven and yet curated and shaped by staff/super users.
The personal/visual support - I always like how questions/suggestions are answered with a screenr, and answers, especially staff ones, are mulitple links. This makes it easy to follow, but also conveys the personality of the staff and how approachable and supportive they really are. Think about how you can do that with yours
How to apply this to your own community?
Think of it as an instructional design challenge, not just a "how can I make my community as great as Articulate's", which might be hard. For example, when I managed a group, I used to do an email round-up to demonstrate the value of belonging and participating in this particular online community b/c my users were more email users than community/forum users. That might be a way to ensure people are involved. Think about it as a part of your instructional strategy and maybe check out Innovative Performance Support as a way to design it. This is a blog post that describes their 5 moments of need approach: http://performancesupport.blogspot.com/2007/11/beginning-discussion.html
The pay-it-forward culture is not just staff, so as Tom noted above, model what you want and encourage those things when you see them. I'd read "Switch" by the Heath bros http://www.heathbrothers.com/switch/ for some great inspiration on change, which might help.
Hope that helps Kat, but please realize that there is a bit of magic in this community that might be really hard to duplicate!