First off, Plasma's are the best display technology available today. Don't let anyone tell you otherwise.
Secondly, what you are seeing is called "ghosting" or "image retention". This is temporary. It'll resolve itself by you just watching different material for a while. If you want to speed it up you can leave it on a channel that only produces static for a few hours and it'll disappear.
Come back here and update us when it's gone.
WOW! Blast from the past over here.
A quick update then: On the second week of December 2011, a bright red line appeared on the right hand side of the Plasma display. It was a defect that went unnoticed, and then we panicked and performed the Warranty Claim in mere hours before the Samsung Tech Support closed up for holidays.
They exchanged it with a 55" Smart TV LED-LCD. Free upgrade!