Bad news - effects are real, and cannot be 100% predicted. No matter how much or little you play, there's always some chance of burn in.
What you can do is minimize the risk. Most important thing is to make sure it is adjusted properly - especially keeping things like brightness turned down to proper levels. Next thing is to make sure you mix stuff up. Don't always play the same game.
I received some real good advice from the guys in the RPTV forum. For every two hours of gaming you do watch a movie. Same goes for watching movies that still show bars (2.35:1). If you watch one make the next one one w/o (1.85:1). What you are basically doing is erasing the effects of static images with moving images.
Keep in mind that burn-in is uneven wear. This is cumulative over time. If you spend 50% of your time viewing the same bright static icon, regardless of what you watch in between, you can bet that eventually that area will wear unevenly. It's not as if flipping on something else after a long session just wipes out these cumulative effects. Obviously burn-in can be very overrated but it has happened to people. If you are after a dedicated gaming monitor you might consider something else especially if you think you'll be playing a lot of the same game (think DLP or LCD based sets). If you are an all around user that wants to enjoy some gaming along with DVD, SD, and HD then you will likely never encounter an issue so long as you set brightness and contrast correctly (AVIA or DVE calibration DVDs).
Incidentally, movies filmed in a 1.85 aspect ratio will show black bars depending upon overscan settings as a 16:9 ratio is 1.78. Those that tweak their overscan settings to lower levels (increases amount of information/resolution in the viewable area) will see them.
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