The following is of interest primarily to those who live in the US:

It seems every day some company or another discovers one more piece of data they can lure people into providing them with.

It started with our email. Hotmail, Yahoo, and eventually even Google attempted to lure us into providing them with all of our digital mail. They touted its benefits (safe! automatic virus scanning! access from anywhere! no need for backups!) and tempted us to give up physical control over our email.

Next they wanted our pictures. Picasa, Flickr, Kodak, snapfish and so many others touted the benefits of storing our pictures online. With one click, you can order prints! Share with your friends all over the world! Free organization and editing software!

With the advent of social networking, they now wanted us to store our very thoughts on their servers. Tell everyone what you are doing right now!

The future brings applications that promise to store your documents and other files. As everyone moves to low powered netbooks and the desktop slowly issues forth its dieing breath, they want even our computing power to be provided by the cloud.

I'm not trying to paint the portrait of some grand conspiracy. All of these advances are positive and the trade off is worthwhile for most people. Provide marketers with more data on your interests and not only will they provide you with free services, but they will also make sure that advertisements you see are for things you are likely to enjoy! For most people, this is a fine deal. But maybe not so for us.

What we, as individuals with unique privacy and security requirements need to understand is that by giving up control of our data, we are (among other things) making it easier for our enemies.

If you are in the US, there are two different legal documents that can deprive you of your right to privacy. The first of these is a subpoena and the second is a warrant. To most people, these terms are interchangeable, but legally they are not. It is important to understand the difference.

A subpoena can compel a third party to provide information that is of value to an open case. Lawyers issue subpoenas directly with virtually no oversight. Thus, if I am interested in obtaining all of an individual's email from his gmail account, all I need to do is sue him and write up a subpoena that the court clerk will stamp for me. Other than minor administrative costs and whatever fee Google wants to charge me for troubling them, that's all that is needed to obtain all of the email that is kept in a third party server.

However, if I want to obtain all of your emails which you keep on your personal computer, I have a problem. The fourth amendment of the constitution protects you from unreasonable searches. In order to obtain all of those emails, I would need a warrant. The bar for obtaining a warrant is much higher than for getting a subpoena. No longer can I just type up a paper and go to the court clerk to get it stamped. Now I must go before a judge, prove to him that there is probable cause to believe that there are emails in your computer which will implicate you in some crime, and have the judge issue a warrant. Obviously, if I'm not with law enforcement, I have no chance of obtaining this.

There are many arguments for keeping your head out of the cloud. I was only interested in addressing the legal aspect because it is an argument that requires some specialized knowledge that most people don't have, but there are countless other good arguments that can be made based on privacy and other aspects.