While popular, Dropbox continues to be an ongoing source of angst for lawyers who would like to use the cloud, but are frightened aware by security concerns. See Dropbox Security Concerns? and Dropbox Privacy Policy Changes (Again).
Thankfully, the ABA Site-tation has come to our rescue by pointing to these helpful posts from Nerino Petro, Futurelawyer, and Lifehacker. Thank you ABA Site-tation!