Certainly specific tv/monitor daily usage has a huge effect on how images may burn in, but for most folks, it is rare that you never change a channel. It is equally rare that you let your kids (or perhaps even yourself) play an xbox game for tens of hours without ever turning off the set or doing at least one different thing with the tv between gaming breaks.
As with any expensive electronic component (lets say more than $300 just to toss out a number), the home owner should know how to properly care for their unit to give it the best longevity possible. If for some odd reason a home owner required to watch CNN each day for tens of hours, and only CNN, then i would say they are the odd few that should look into the serious issue of burn in before they commit to a certain technology for their home projector. You see these changes in monitor types in newer airports across the country.
I really don't think that a standard use of a plasma tv will burn in an image with watching CNN for ten hours straight. Perhaps a couple weeks of 24 hours a day will produce some results, but again, if plasma tv were really easy to burn an image after a mere couple of hours use, no one would buy them and you would have heard alot more about plasma tvs being returned by now.
