A few of my friends think this morning's twitter/facebook hoax was a good thing! It "raises awareness" of terrorism: they got really angry and passionate about it as if I was a fool putting everyone in danger by listening to the real news. They actually accused me of not caring about my F&F who use the tube because I said the hoax was a hoax (FWIW I am in London and we all use the tube). 
Basically the way I see it, it panicked a load of people needlessly, diverts attention from what the police are actually telling us to do, could mean people focus on the tube when we should have our wits about us everywhere (and say someone wanted to bomb a bus... how could they make it crowded? Scare everyone off the tube) and could lead to "the boy who cried wolf" later.
And all for a sick joke.