Haven't had much time to play with my new XL4, as setup and cable card activation was finished only a handful of hours before we left for a weekend away from home. One thing I did notice, however, is that when I was channel surfing, my system had to re-sync the HDMI every time I flipped to a new station.
I have a high-end Onkyo preamp, with everything connecting via HDMI. The preamp sends video out to an overhead projector or a Samsung HDTV, depending on which I am watching. The sync issue appears to happen equally on both displays.
Basically, when I flip the channel, the screen goes black, the name of the input "Video 1" or something pops up for about 1 second, then the picture reappears. I have yet to actually see a problem with the system being able to find a good HDMI sync, but it is definitely annoying that it has to re-do it each time you change the channel.
This did not happen on my Dish Network box hooked up in the same way (VIP722). On there, the channel just changed, without the name of the input and the black screen showing up.