Breaking in a plasma has always been a 50/50 thing. Half the people say you absolutely must do it and the other half say you don't, it's not necessary.
Here is a CNET writer's take on it, he too says that you don't need to;
Personally, I have a plasma I bought 5 years ago that I never broke in, I didn't know about it then? I pulled it out of the box, set it up and proceeded to play about 4 hours of Xbox on it, the absolute worst thing you can supposedly do to a new plasma. 5 years later it's my daughter's gaming and Roku TV and looks as good as the day I bought it.
.Edited by Straybeat - 10/12/12 at 10:42pm