DotNetNuke has a lot of registered users (A LOT!), but the KB is very unusable.. it's pretty hard to find something in the website, the general search engine work pretty bad, the forum searh engine is even worse. I see so often the same question again and again because you can´t find the answer in the system.
The useronline module make false stats, with an unrealistic connected users. (It's a known issue)
I do recommend, take a looks to other KB community and do something if you want to keep users active. For example, take a look to www.dpreview.com, this is a photography community, with much less user registered than the DNN, but much more active (a lot more). the KB work great, if you have some issue, you find previous post, with solutions and the community respond quite fast.. but not here...
Are you aware about this situation? (What's wrong with DNN community?)
You have the stats...so how many unique users post in the dnn forums a week?, how many users looks for something in the KB, how many users find something?...
The dnn team is doing great work for the framework, but not as good for the community....
that´s my 0.02 cents