Features used by 80% of social sites | Acquia

Features used by 80% of social sites | Acquia: "Blogs
Forums
User profiles
Commenting
Ability for people to get notified when comments are made on a blog post or other content
Share this links to encourage visitors to tweet about posts on the site or to share with people in their social networks
Follow us links to encourage site visitors to follow the site on Twitter, Facebook, Flickr, and other networks
Mailing list sign-up to let visitors join an email list"

'via Blog this'