I also had the problem and I am really upset about it. My neighbor was getting FIOS installed yesterday so I had the opportunity to talk to the guys doing the install. Seems that when they rolled out the new IMG, it is doing this. I understand from the installers (who also have the problem on their home tvs) that they were aware of the problem and were trying to fix it. I got several calls from FIOS technical support including one recorded message that said it would be fixed by jan 23! I wonder if that is true.
Anyway getting back to the issue. The problem is supposed to be associated with HDMI and the new program guide. It gives you the green line on the right side and if you look on the left side you will see the picture distorted, like a beveled mirror, for about 1/2 inch (depending on the size of the screen, mine being only 42"). When you use component cables rather then the HDMI the problem goes away. I did notice the pq gets a little worse when you do this, most likely due to the component connections being analog. While I can live with a "smoother picture" I no longer get surround sound from the tv so that option really didn't work well for me. Another solution (the one I am using) is to go into the stb and change the ouput to 720p. This eliminates the problem with the line on the right and left and also allows me to get the surround sound. The down side that I noticed and that might just be me, is that I am not getting some distortion (or whatever you call it) on fast moving activities. For example, watching the football games, I got that lag which I didn't have when set to 1080i using either the hdmi or cables prior to the IMG change. I did notice the problem only exists on some stations not all of them.
So, until it is fixed, I will leave the box output at 720p and let the tv upconvert it to 1080i.
Hope that works for you