There are many examples of communities built without forums, or before forums were ever added. Often this can be through a different kind of process of interaction than what a forum typically facilitates, and often it is just within comments to certain blogs.
Has anyone built such communities and what are your experiences?
Well, the original communities were bulletin boards.
Today, there is still IRC.
And thousands of sites on the net that are not forums, but communities (facebook, million facebook clones, etc).