Lawyerist.com takes a cursory look at cloud computing and confidentiality. Sam Glover did some investigating and the results were mixed. He says ultimately "it is still up to you to learn about the security of the systems you use and assess their suitability to your clients’ needs."
One thing lawyers need to keep in mind when deciding whether to use technology that stores your clients' information on off-site servers, is that your own computers all have connections to the internet. Don't automatically assume it is more dangerous to use the cloud than your own computers. Chances are, the cloud computing company employs much better security practices than you do, yet attorneys often don't think about that simple fact. You must do the hard research to determine that your clients' data is protected, whether it is stored within the walls of your office or not.