An aquaintance of mine actually did it. He is an ATC as well. Said he got distracted in his walkround by someone talking to him (not an excuse). Took off from an uncontrolled field but on landing controller said "whats that hanging from your aircraft?". He said it didn't feel particulary different. I would imagine even a 20ib lump of concrete bouncing along a runway you might feel something and /or even bounce into the hull and cause damage.
From that day he has never flown since. Says he realised he came too close to meeting his maker, to ever go up again.