If your website is just a small-sized one for private business, I don’t suggest the forum.
As other friends already mentioned, a forum should be built on the premise that the website attracts thousands of visitors everyday, but, generally speaking, it’s really hard for a new small-sized website to achieve such a goal, so, if there is no large traffic, there may be few users who register to join the forum, which is not realistic.
However, it’s a must for large-sized website.
I've got an example.
Through the link: http://www.brush-machine.com/FeedbackList.aspx
You could see a list of messages left by different visitors, along with administrator’s reply.
Also, on this page:
http://www.brush-machine.com/products/2-Axis-2-Head-Brush-Drilling-and-Tufting-Machine-WXD-2A2H01.htm
At the bottom of the page, you could see the similar information.
Obviously, it’s a kind of interactive communication between website and users, but is not official "Forum", which, I think, is quite suitable for small-sized website.
