Social Groups are BAD BAD BAD. Everything you add to your forums, there are two things you should ask first...
Will your users use it? I like to think of this as the Albums question. Will your users use it? Some forums, yes; most forums no. For most forums, users would much rather use FlickR, PhotoBucket, ImageShack, etc than the forum album.
Does it take AWAY from your forums. Generally, everything you add to your website, you add because you want to draw people to your website. Social groups DO NOT do this. The only people who use social groups are those already on your website, and even then, only a bare minimum percentage of your users. Having social groups actually detracts from your forums because it takes content AWAY from your forums, where new users and guests will see it, and segregates them into their own archaic section.