[Bob]

As I understand it, image retention in plasmas is most likely to occur when the display is new (something about the display cells having to "age" for a bit before the risk drops). For both of mine, I ran the "burn in" sequence from AVSForum (just a series of coloured screens that loops endlessly) for about 100-125 hours before I started to use them. Both my TVs also have a "video pattern" mode (sometimes called a "scrubber") which will display a scrolling white bar for 1 hour, then turn the TV off--such things are supposed to help reduce retention.

That said, my older plasma now has image retention from too much Rock Band, and I think it's actually recent (I might have been playing without the image orbiter on, whoops), so it's still possible to cause, it seems. It's very faint on that screen, and really only visible with a solid grey background, but so far the "video pattern" hasn't done much. Newer TVs are apparently better, but image retention or uneven wear is generally possible on pretty much every display technology.

AVSForum has loads of guides for such matters in their Plasma forum, sometimes even model specific (such as what brightness/colour settings to use for the first 100-200 hours). I used that extensively when I got mine.

Edit: Also, EA Games (Madden, NHL, etc) are apparently really bad to use with a new display. I heard of some guys with last years Panasonic plasmas that had noticeable retention after only a few hours of Madden. Those perpetual bright logos with hard edges are to blame.