Thing is, if they decide they even want to try to look into those things on you, you're already busted, you just don't know it yet.. Its not feasible to put word recognition software on drug related topics.. They'd be flooded!!!
There are crazy computers possibly eavesdropping on you, but they're looking for intelligence based stuff, not stoners.. It would probably be riskier to text a friend saying 'I just picked up some bomb shit man', than 'Meet John smith at 123 Fake St at 4:20pm to sell him 2lbs of marijuana'..
http://en.wikipedia.org/wiki/ECHELON

George H. Bush Declared a "War on Drugs" during his term in office. George W Bush passed the Military Commissions Act of 2006 which suspended Habeas Corpus, and gave the government the right to declare anyone they want a "non-enemy combatant", hold them without charge, or council. (GTMO) It was intended to be used to protect us from terrorists, but it is not inconceivable that Homeland Security could also interpret that as resistors in the War on Drugs. I mean, the War on Drugs has been declared on the American People for decades, right here in America. I forget how many days the official "war" in Iraq lasted...

Unfortunately there is no means of electronic communications that is safe. Technically you added your name to their list of possible "non enemy combatants" the moment you registered on this website. How many other things have you done or said that could call attention to yourself? How much attention would you need to draw before they pointed satellite cameras at you so sensitive they could tell you how much change was in your pocket? Getting busted would put you under permanent scrutiny. Especially if they tell you it isn't on your record. Wise up. The war on drugs is a huge cash cow for the government. Why would they go and screw everything up by legalizing weed? Even if legalization generated more money, money is created out of thin air these days. Busting people puts human souls on a string for years. Jailtime, awaiting trial, sentence, probation, fines, etc. Absolute control of lives. When money isn't worth anything, what's the next best thing? POWER. Will legalizing pot generate POWER? No.

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Why Live in Pain?

If America has declared a war on drugs, and they're losing the war, then I guess that means the most powerful country in the world is getting beaten by a bunch of stoners and junkies huh..
(Paraphrasing Bill Hicks, I forget his exact wording)