Here is Panny's 2010 stance:
"When your plasma TV is initially installed, the first 100 hours of use is known as the "break-in period." While there are no special requirements for the break in period, to minimize any risk of image retention, you may want to be aware of the following information, 1. Make sure the plasma TV is in a viewing mode (aspect ratio) that completely fills the screen. The panel is shipped in this condition, in what is called the "Just" mode. 2. Change the Picture Mode from Vivid to Standard or Cinema. Cinema would be best. 3. Briefly engage the 4:3 aspect and confirm the side bars are set to "Mid", or "Bright". This can be adjusted in the Set Up menu. 4. Always return the display mode that fills the screen (such as Just, Zoom, Full, or H-FILL). 5. Try not to view channels with stationary backgrounds or logos for extended periods of time. 6. Avoid extended display of static images (video games, computer images, DVD title screens, etc.). No fixed image should appear on the TV for more than 15% of the viewing week."