I never advocated the engine block thing, it was invented by Abbie Hoffman as a form of civil disobedience. I don't condone or condemn it.
He also went into companies he didn't like with an electrical cord with a plug on one end and loose wires on the other; he would plug one end into the wall, and the loose end he would stick into the company's telephone jacks (this was before modular jacks, I expect, or he wouldn't need loose wires at the end). He would do this while he was in the waiting room, most often.
And no, metered mail is weighed by the post office if it is over 1 oz. And no, the credit card companies (or whatever) don't pay for every envelope they send out, they pay for every envelope that is returned.