The whole break-in period is a matter of opinion. Some say break-in isn't necessary, others say you should follow it until the phosphors have settled in. I didn't take a chance and followed it for the first 100 hrs. ("o" setting on picture, not using "vivid"; avoiding 4x3 viewing, static images and logos; etc)
Here's what Panasonic says,
"Burn-in," or image retention, is an uneven aging of the phosphors in a display device, can occur on any display that uses phosphors to generate an image, including tube TVs, projection TVs that use CRTs, and plasma TVs. Such uneven aging happens when bright, static images are left onscreen for an extended period of time, which can leave a visible "shadow" effect.
Improvements in panel service life to over 60,000 hours have minimized the risk of image retention. In addition, screen savers, pixel shifting, and brightness level adjustments can dramatically reduce any chance of image retention. Use common sense when it comes to your plasma TV; don't pause video games or watch TV stations with station logos onscreen for long periods of time, and use one of the many display calibration DVDs available today for properly setting brightness and contrast.
The rule of thumb: if you don't worry about your traditional tube TV, you don't have to worry about a Panasonic plasma TV."