That does not look very good at all. I would check with another 1080p signal, like blu-ray, and see if the problem is there. Also, try and change to another HDMI port and cable. Maybe that one is bad? Lets here from some other posters, and give it a day or two. You may have to return it..
Maybe the scaler in the 360 is bad, and is adding artifacts?? Any way you could try someones Xbox? Tell them 'byo-xbox' and have a gaming party with the new 58!!
IT IS JUST MY OPINION!!!!!1