I have a 100" flat screen between my speakers. I was very worried about the effect it would have but I use a Lyngdorf processor with their seriously amazing "room perfect" correction software. I know purists will balk at that but the system is not complete to me without a TV. My favorite use of my dedicated room is watching concert videos (on disc). The Lyngdorf, unlike most lesser processors, allows the main speakers (Focal Sopra 1's) to retain their unique sonic character instead of trying to force them to bend to the processor's will.
I also have a very large rectangular ottoman in the room and I found that even without processing the signal if I push that up between the speakers and right in front of the TV it helps with quashing the undesirable reflections.
I once read right here on Audiogon that a member claimed that the flatscreen didn't hurt his sound nearly as much as he feared. In fact, he said it actually helped preserve the center image. Since I don't use a physical center speaker (processor has 16 channels, configurable to whatever you like, I have a 8.2.6 configuration) this helped assuage my worries. I just don't think about it anymore and my room sounds like a dream. Literally. I've been dreaming of having a room like this for 40 years.