Well Danni the thing is , it isn't easy to get sued for. The only server i have known to be sued is Wowscape where the owner was making 500 grand per month while the server cost 10 grand a month. Every other server that was target got a cease and desist email, some continued regardless and blizzard took no action. A lot of people posting here are speculating stuff which doesn't even happen. Donations are nothing to do with blizzard unless they are being used as a profit ( something other than server upkeep / development ), if we follow the same logic, notch could take down any server because he hasnt given any right for minecraft to be used to make a profit, but it just doesnt work like that. Donations are not profit. There are over 100,000 world of warcraft servers, practically all using donations, and the only one sued was Wowscape. So going by past events the chance of being sued would be something close to 1 in 100,000+ , its like winning the lottery. Im sure the people who play private servers know exactly what im on about, its the people who think there are just a couple servers here and there, but the reality is there is tens of thousands.
EDIT: Also if there ever was a legal issue, its as simple as taking the server down.