Hi,
first of all congratulations, it is a service I love and I follow some of the blogs hosted by you.
I've always thought about wanting to start a mini blogging platform similar to yours but I've always been stopped by this: how do you moderate the content? if someone posts something illegal, how does it work? if illicit messages or photos are posted, of whatever form, isn't it a big deal to get out and let the police know it's not your fault? is a simple disclaimer of reponsibility enough?
They bought something with your ref, you should have a piece of the pie, period.