I'm seeing some great implementations around niche communities in finance sectors, based around spiritual interests, political and sports. Some are growing really quickly now, it's great to watch. Most of these successful sites are straightforward, using Discussions and Messenger/Chat to foster group and PM interactions.
We are planning on developing our UNA Learn LMS to bring learning functionality into the mix as part of UNA 11 - so this will be another tier of possibility that I'm confident will bring increased scope into many of your sites.