I know you're suppose to mount a tv near or on a wall, centered horizontally...Then put on sofa or loveseat two thirds back from the tv, also centered...What do you do if you have a loveseat and a sofa?
If the room is smaller you could put the TV in a corner and the couch and love seat on the opposite walls. I like the idea of having chairs on the sides of the TV, never had a room big enough to do that but maybe one day I will.
The only other thing I can think of is doing theater style seating with the couch behind the love seat on a riser (both facing directly at the TV that's centered on the wall. That would involve a lot of work and is probably not what you are going for anyway.
Also, you don't have to put the seating 2/3's back from the TV. It doesn't matter how big the room is, it matters how big the TV is. I googled "television+seating+distance" and found this nifty little chart (ok had to provide a link because it had to many "images") just scroll to find the chart.
Wide-screen TV-viewing distances
You'll notice that we said regular televisions. Wide-screen televisions showing high-resolution DVD and HDTV look better than regular sets, allowing you to sit closer and experience a more immersive, theaterlike picture.
With wide-screen sets showing DVD or HDTV, you can sit as close as 1.5 times the screen's diagonal measurement and still not notice much of a loss in quality, while sitting farther away than three times the screen size means you're likely to miss out on the immersive feel. Here's a rundown of minimum and maximum recommended viewing distances for wide-screen sets.