Modern Plasma as Computer Monitor?

Depends on the plasma, but in general yes burn in will always be somewhat of an issue with plasma's because each pixel is like an independent bulb with it's own lifespan, so the ones that get used the most or brightest are going to dim or discolor the soonest. They do things to mitigate it now like shifting the picture slightly every so often, but with a solid white or grey bard at the top or bottom of the screen it's going to burn in eventually. Plasma's excel at fast motion video but are not really suited to be computer screens, which is why they aren't marketed for that. If you're talking a few hours a week then you're ok, but if you're talking a couple hours a day everyday IMO you're better off with an LCD long term.