My env.: WInXp, IDE 1.0.3 , Mega 2560 Problem: IDE hangs when sending program to arduino board. Hangs mean that progress bar get 95% and stop. If disconnect usb, IDE continue work as usual. Reason: thi ONLY happen if program have 3 or more "!"
For example:
Serial.println("Huray!!!"); - hangs
Serial.println("Huray!!"); - sent and work ok.
I'm not sure you would call it a bug. That is the signal you want the bootloader to enter a diagnostic mode. You can avoid that by using the ICSP to program it if you feel it is absolutely necessary to upload "!!!" in your code.