The personal anecdotes seem to be pretty helpful to others here, so I'll share my own experiences.
I had a Panasonic 4:3 RPTV for three years and I've had a Toshiba 16:9 RPTV for almost a year now. I play a good deal of video games and watch movies every now and then, and my viewing is naturally varied. I watch a lot of ESPN, a lot of network prime time, and record all sorts of stuff on my D* Tivo. My SD viewing (which I'd guess is around 25% now) is ALL done in stretch/zoom mode. My current set has had no more than forty hours TOTAL of viewing with 4:3 bars on the sides.
I have had absolutely no problem with burn-in on either set. The Panasonic was actually given to me for free because it had some issues, one of which was a slight burn-in of what looked like a DVD menu. I don't know what the heck the previous owners did to that set to cause the burn-in, but I couldn't replicate it. I tend to play video games in streaks and I may not change games for months at a time. This means that the same HUDs, gauges, bars, and meters are on the screen repetitively. Sometimes I have an hour to play a day, sometimes I may veg out and get in five hours in a day. Some days I don't play at all. None of these graphics ever burned in to either set, including the one that was evidently prone in the first place. I don't take lengthy breaks while playing, and on the rare occasion I do, I turn off the set.
I've never had my newer set calibrated, and the contrast is set around 50. No problems with it after almost a year and probably (I kid you not) over a hundred hours of Madden played on the Xbox.
The original post is right on the money about varying your viewing habits. I watch all types of stuff not because I feel compelled to, but because that's just the way it works out for me. I don't use the 4:3 mode except for the occasional video game or SD football game. Everything else I watch in SD is of so little importance that I really don't mind it being stretched (and Family Guy looks great stretched, anyway
). I guess I'm lucky in that everything I really want to watch is in 16:9.
From my own experience, you literally have to play video games or watch channels with tickers all day, everyday, to see burn-in. I have by no means abused my sets, but for the amount of time they've been in use, especially with video games, I've seen no problems. A little of this and a little of that, and you shouldn't have any problems.