Getting your visitors to create content for your website is a Search Engine Optimization gold mine when you can get it right. Here's how.
There are plenty of ways to get users generating your content - Quora, after all, is content almost completely driven by users - but it is not nearly as straightforward as most people imagine.
Works best if your content is controversial as this motivates users who want to express their point of view. If you have seen blog comments that are just endless "Thanks for that great content" this doesn't add anything of value to your page. In fact it is more likely to polute the context of your content.
You'll also have to make sure you check every comment before it gets published as commenting systems are a magnet for spammers who think that if they put a link there it will actually count for something. Platforms like Wordpress have these moderation facilities built in but don't forget the time factor.
They can reflect on you badly if you don't take time to interact with your commenters which can take your attention away from creating new content for your website.
All this said commenting is usually one of the easiest things you can add to a website that will generate user content so it is well worth trying.
Undoubtedly one of the best ways to have lots of text, and original text, added to your website is to put a forum on it. Users can discuss things there which makes for lots of original content and often very useful content that others will link to.
However forums can have disasterous and unexpected side effects:
Forums also leave you in little control of what keywords will start to dominate the pages. If you sell bicycles but your forum becomes better known as a place to swap tips on repairs then your website will become better and better known for 'how to repair a bike' and less and less known for 'bicycles for sale'.
The upshot is that forums as bolt ons for websites unless you have significant resource to manage them. Even in this case I generally place them as subdomains to stop them polluting the context of the main site.
Really this is a similar situation to a forum and once again there is a great deal of administration to do here, often unpaid.
Without proper promotion they look ghostly and empty but in any circumstances you will battle endless spammers (or even spam robots) trying to post links to whatever they are currently spamming.
Reviews are a little easier to moderate if you limit access to the visitors of your website who have actually purchased something. If you leave it wide open expect to do battle with spammers!
I'm Tim Hill, a Search Engine Optimization and Online Marketing specialist. I created this site to help others understand that SEO is not a mysterious black art!.
If your a newbie try the Getting Started in SEO page, otherwise feel free to dig around and learn more.