Despite what anyone here *suggests, read your tv manual and follow its instructions first.
You will encounter image retention (IR), and some will wipe clean faster than others, but most if not all IR will fade. The tv will typically get better with some age (months rather than hours I say).
Your manual will tell you how to activate the pixel shift function
I play 360 on my Samsung plasma and I started right out of the box, break in is a clique rather than a fact, do some reading here and make your own mind up. I do get IR but it does wipe away in less than 30min (7 legendary Halo hours trying to kill two F%*(&^ Scarab tanks). Permanent burn is nearly a myth, in fact the only perm burn I have seen is on early plasma models used as leaderboards and baggage claim wards, and I bet that would wash away nearly clean after some good tv viewing.