OK.. Since Artashes allowed the thread to live, lets add to it.

Since I'm not a host, I cannot say if running a forum helps the host, but since I have a keen interest in the shopping experience, I must say that I like it when a host has a lively support forum, even if it's not entirely dedicated to support/presale questions etc.

As a prospective customer you get to read how things were solved, how fast they were addressed (though that's not always a good measure because of PMs and because some hosts clearly tell their customers that the forums are not manned 24/7), if the customer was treated with respect and if the customer was satisfied with the solution.

If things are kept in order, I believe a forum can be a great tool to close more sales. It says "this is how we handle things" and it allows non-customers to get a feel of how it is when you are customer of that particular host.