Plasma's prone to burn-in in video games. Here are a few good articles.

Plasma especially, but even a lot of older rear projection tv's still have a problem. But most have really worked out this issue.

Really? I'm still leery because if you get burn in, you're screwed. There's no way to fix it, right?

Yeah pretty much, you have to really research the model that you have, it can vary. But the burn in happens because the avatars/icons/HUD are exposed in one location for a very long time. Look ...

How long does that take though, an hour, 3 hours, 7 hours? doesn't it take a real extended time, like days?