I've posted about this before, but I'll post it again. A few months before the first Obama election, there was a thread on Slashdot about things you couldn't say on the Internet. I humorously contributed "I am going to kill the president" to the discussion. A few months later, the Secret Service showed up at my house, with guns, to question me about it. (The agents were quite reasonable about the whole thing, FWIW, but they did need to follow up after reading that comment.)

People are watching you, so be careful what you say.