Mine is cracked as well. Just as you describe.
I purchased a 50" plasma tv made by samsung about 4 months ago (April). The unit has a 1 year warranty. After just this small time period, the tv blew up while I was watching some movies. There was a loud pop, the picture faded from right to left and the sound became nothing but static noise. The screen cracked horizontally right above the control buttons when this happened but it is on the inside part of the glass not the outside that you can physically touch. I found a man on the internet that had the same problem and more than 20 others online that have reported the same problem. Samsung has refused to repair the unit, stating that the panel has "physical damage". Of course it does, the unit self destructed and blew up! The tv was never moved from its original location at delivery and does not have a scratch on it. The outer glass of the screen is blemish free. I have tried to resolve this nicely, always waiting for the call-backs that never happen, but my patience is running very thin.
This is obviously not a new problem given the number of people I have found experiencing the same problem.
My service ticket number is 4005422253.