My older brother used to work for NSA, they have equipment that can listen in on any cell convo in the world. But, they are not allowed to listen in on domestic, only international calls. So its definitely possible to listen to cell phone calls. If you really wanted to get paranoid, they could even shine a laser beam on your window and hear every word you say inside your home without even going inside. This is because the windows vibrate a tiny bit from sound. They can do this from off your property.

I agree though, don't say anything incriminating in any way that can be stored. E mail is pretty safe - the simple volume of e mails going over the internet make it next to impossible to intercept. However, that being said, if they wanted to read your e mail I doubt it would take them long. But, the random interception of an email by a DEA officer is really impossible. Remember though, on the internet you are NOT anonymous. Everywhere you go, you leave your IP address. If you are on a public network like a university, you are safe. But, if you are at a home network, it is technically possible (and would only take a few hours work) to track a poster to an actual home address. Legally though, I doubt they could do anything with that as really anyone could be using your computer or internet. Theyd have to prove that YOU typed what was sent from your IP address, and thats difficult so they don't pursue those methods.