I need all of your help because Adelphia and Circuit City are worthless! I recently purchased a Sony Trintron 30" HDTV. When I set the HD box to the 1080i output, I get a shaky picture...actually it's more of a small vibration. Upon switching to 720p, everything becomes clear. I've switched HD boxes 3 times, switched cables, and even exchanged TVs!
When looking a stationary picture such as your guide data viewing it at an interlaced format will make it seem jittery. This is one advantage of a progressive display. If you look at scenes that are changing slowly this jitteryness (is that even a word? ) will not be observeable.