Was there ever a time when mining on Amazon EC2 was profitable? When the difficulty was low, so was the exchange rate, so I'm not sure.
Now, no. In the past before GPU mining when everyone was mining with CPUs the more CPU power you had the faster you could mine. The problem was that the exchange rate was so low that it wasn't profitable at the time.
If you had mined then and lost money you would have made up the difference at current market prices.