We had a case recently where a PR company decided to tackle some negative comments about a client on a popular negative forum.  The backlash was immense and completely back fired.

Here are the main reasons for not tackling forums.

1. Forums are traditionally places where people like to complain, the last thing they want is someone to defend the company, their attitude is you can put your positive info some where else.
2. You can’t control the content on a 3rd party forum site so its really risky, any thread you begin will start out positive but will quickly attract negative content.
3. Last but not least, the most important reason, by adding more content onto these types of sites you encourage Google to rank it higher.  Especially if it attracts more people to attack the company and add even more content.

The PR companies  intention was good, but you cannot apply the same methods you would use in publications (Traditional PR) to the Internet as you will get hammered.

Also sites like Wiki and  Facebook can bite you if you are not careful and incorrectly set up.