iMac was knocked off a teacher's desk and the glass was cracked and broken off in a few places.
I have two words: Easy. The instructions were easy to follow and with the suction cups, the broken glass was replaced without a hitch.
When removing a cracked glass, cover it first with some gaffers tape or masking tape so that it all comes off in one piece. Just don't forget to leave space to attach the suction cups.