The short answer is maybe.  The longer answer is if you have time to maintain them, then the answer is, “hell yes!”  You also need a decent product, if you’re selling a shitty product and you get a lot of complaints it’s probably not a good idea to have a public complaint area.

Forums need to be maintained.  A lot of companies have forums where staff never show up.  You’ll find you are getting a lot of complaints from customers or future customers when you don’t have someone in that section of your site doing damage control.  A good forum moderated properly can skyrocket your business.  If someone is curious about your product or service they just go to your forum see all the people raving about how great your super squeegee is, they get their questions answered by other product owners or your staff and they end up buying.  Now since this person looked at the forum in the first place to make the decision it’s possible you’ve earned yourself another forum member.

A company forum doesn’t necessarily have to be busy to be a success.  I’ve in the past used a closed forum for an FAQ section to a site I’ve owned.  It was great because it had all of the functionality of a forum, it answered everyone’s main questions and I was also always able to promise that the forum would open to the public soon.  I never really opened the forum because the site is kind of a hit and run type of product.  It’s a one time sale with no hopes of a re-order or any other future business.

Forums and blogs rank very well in the search engines.  They are great for quickly and easily adding new content.  How much easier can it get than just typing out what you want and pressing Post or Publish?  You don’t have to worry about formatting or any other issues, everything is handled in the built in WYSIWYG editor.  The search engines know these types of sites aren’t static so they keep coming back to crawl the site and see if there is any new content.

Blogs are great, you can moderate all the comments made without looking like a big dictator and it doesn’t normally require as much work as a forum.  They are also very flexible you can base your whole business site off of a blog with very little if any modifications.  It’s possible with a forum, but you’d have to add some kind of CMS functionality to it.

Popular/Best Forum Software:

VBulletin.  The best out there in my opinion.  I always make sure I have a few licenses at my disposal to quickly launch forums.  Paid software.

phpBB.  This use to be my favorite, now I’m not to sure what place I’d put this one in.  It’s free.

SMF.  A solid software that’s also free.  This one seems to be getting more and more popular by the day.

IPB (aka Invision Power Board).  I have a license for it.  It works, I don’t know if I really care for it though.  I’m so use to VBulletin that I personally don’t care for this one.  This is a paid forum software.

MyBB.  Originally made to be a VBulletin-like clone.  It’s pretty solid although I’ve heard development is a little slow on this one.  Very nice looking, does look very similar to VBulletin.  Free software.

Popular/Best Blog Software:

WordPress.  The end.  Game over.  There is no competition.  WordPress is free, easy to customize, a million free themes and plug-ins out there (and some great paid one’s).  Can’t be beat right now and no one is in their league on the blogging end of things.

Remember because a script/software is paid don’t think it’s better.  A lot of things are a matter of preference.  Paid doesn’t necessarily mean better.  You can get away with using a free forum script without any issues.  The people that are really the most anal about free forum scripts are webmasters and very savvy internet users.  The casual internet user could care less about what script you’re using.  My motto is if you can do it for free, why pay?