Group message structure ensures close contact and solidarity among members. Mass mailings to all the members in a group ensure that everybody knows what's going on at the same time. The only site to let you bulk-invite people to your group. The only site with a personal and a group calendar. Hard for visitors to find an active public community to join.
Polls are easy to set up and provide a good deal of info.
No chat room for team collaboration. Site is graphics-heavy, which makes it slow to download. Difficult to find features without left-hand frame list that most others use. You can't set as many polling features as at eGroups. Uses eGroups for its mailing lists.