Guys, EVERYTHING is on your HD, even if it's been erased. Unless you do everything on a separate computer, the information is retrievable.
Bottom line -- don't be simultaneously paranoid and then delude yourself you're cool because you use encrypted mail. There's a 99.999 chance of out of 10,000 that the Feds are watching you... but if they are, and they come into your house, don;t be surprised if those "precautions" you took don't mean dick -- because they won't. Then it's time for a lawyer and be done with it.