Over here in the Netherlands we have a DC hub which only allows access to people in the surfnet ip range. Surfnet is a 10gigabit backbone which connects high schools/universities with the internet. About 2 TB is shared, and all people are on 10mbit+ connections. DC is really a great community app, and I'm glad there's going to be an osX version of it!
I do have my concerns though regarding security. There's no transfer encryption. DC would be even greater if it could encrypt transfers like frex. KDX does.
-Dr. D.