Need Help with Plasma Burn In vs. DLP Decisions

I am researching a possible a Plasma TV purchase (brand is to be determined) but I am getting conflicting statements regarding burn in problems. For example, from watching shows with the 4:3 aspect ratio, will I get burn in where the black bars were? In other words, how long can I watch these channels before I MUST change the channel to a full screen display? I have about 12 HD stations but many are not HD. For non HD stations, I was told to stretch to full display but this seems to distort the view. Does Plasma have other usage restrictions?

Fom a cost view point, does a Samsung DLP TV purchase make more sense than a Plasma? My local Retailer is recommending the Plasma since it looks better but many of my friends have purchased the Samsung DLP (50") and like it very much. Any comments on Plasma burn in and plasma vs. DLP would be appreciated. Thanks