One of the issues with any forum, be that a blog or some other means of collaborative writing is how to interpret apparent disengagement.
Ecademy is a social networking site that maintains a number of clubs each with their own forum and also some general blogs and advertising opportunities through Marketplace.
I lead a number of clubs on Ecademy, including Blackstar, the life members club. In all of these clubs only 1 in 10 members participate, but the research shows that this is typical. One issue that arises is when there are polarised discussions. Often a lone voice arguing against a few vocal people appears to be in a significant minority when the reality is far harder to judge.
Silent people are not truly silent, because they leave trails of data behind them when they view a page. If you capture this data then you know the page has been viewed and if you capture arrival time and leaving time you could even surmise if it has been read.
Is silence agreement? - does the failure to post mean that you agree with the previous post? - of course not.
The problem most forums and discussion groups face is that the views of a few vocal people may not be representative and silence, absence of a dissenting point of view, can be seen as agreement. On important issues it's therefore important to validate that what is being said is truly representative.
So, to be able to truly judge the mood you need to be contacting a representive sample of the membership and not relying on the responses of the vocal few. The next question has to be how to find that representative sample?