I've been permanently blocking all connections from any AWS/EC2 netblock I identify after an initial exploit attempt. I much prefer temporary blocks triggered by bad behaviour, but the constant onslaught from AWS finally got to be too much. In the last several months, blocking AWS has done more good than harm. I don't seem to be blocking any legitimate traffic or users, just badly behaved startups and downright malicious crackers. It was a tough compromise, but so far it doesn't seem stupid.