The burn-in issue on plasmas is something that just won't go away. Manufactures have tried hard to prevent it as much as possible but still, it is a side effect of the technology. There is a group of consumers down under (in Australia) that purchased plasmas before the holiday's and left them on for hours days causing the stations logos to be burned into the screen.

Yes, we know plasma this and plasma that, but there are easy things to prevent burn-in.
  1. Burn-in is most likely when the TV is the brightest making the first 24-36 hours of life critical. Even some manufacture set-up screens can cause nasty image retention. (not burn-in but rather, ghosting for a short period of time.)
  2. Turn down the brightness past 50%. Plus, you will get a lot deeper picture. 
  3. Avoid static images. This does not mean the ESPN banner or ABC logo but rather the Window's Start Bar or OS X's Dock. Use the plasma as a TV because you WILL get burn-in if used as a monitor. If you pause the Xbox, turn of the TV.
Believe it or not, plasmas are not the only type of display technology that can suffer from burn-in. CRTs have always had this problem, (think old school screensavers) but so have LCDs. WHAT?!? No! But yes, LCDs can burn-in. The best proof we can give you is Apple's guide to removing burn-in. It is rare and requires the image to be static longer, but it can happen.

Do not be afraid to buy a plasma because of the chance of burn-in. There are tools and techniques to remove burn-in but if you plan on using the plasma as a TV rather then a computer monitor, then you should never ever experience it.