But since breaking in a plasma certainly won't hurt, there's not reason not to do it either.
FWIW, the 4 yr old plasma in my den has a better picture now that it did before I broke it in. OTOH, I did 150 hours of break in slides on my dad's newer plasma, and I would be hard pressed to tell you what (if any) difference there is in PQ. But I darn well know the phosphors are broken in, considering all the crap my folks watch on that poor HDTV (LOL).
Does the members at CNET agree that breaking in new plasma tv's should be done? 100-200 hours of low brightness and contrast. Getting my first plasma tomorrow. Panasonic 65 vt50.