According to an article from eMarketer - Where Are Social Media Marketers Seeing the Most Success? - forum are still part of the global social media strategy of the Top 500 Companies, and they are still getting really high marketing success with them.
Most people would blindly say Facebook has replaced everything (including our dear forum), but it seems not, and even if Facebook was more used in 2010 (54% for 2009, 85% for 2010), forum are still a very reliable way to promote and increase the buzz around a company or a product. 93% of the companies declared that a forum was part of their social media tools for 2010, 2% more than 2009.
That's a good answer for people that wonder if they should drop their forum to rely only on a Facebook Page or a Twitter stream.