Sync a file via Dropbox and run lsof -i, and you get something like this: ec2-54-221-232-10.compute-1.amazonaws.com:https EDIT: it may be that they use EC2 for

Sync a file via Dropbox and run lsof -i, and you get something like this: ec2-54-221-232-10.compute-1.amazonaws.com:https EDIT: it may be that they use EC2 for their infrastructure, but not for actually storing files. But they still use AWS.