Unless you have a large house with a lot of space, having a dedicated home theater is very wasteful of space. We wanted our room to have three primary uses; as a home theater, as a second living room, and as a guest bedroom.
One of the goals in using the basement was to make it not look or feel like a basement. There were a number of things we did to try to accomplish this.
In the bathroom, there are two windows, one of which faces south. This lets in a lot of natural light. For the south facing window, we put in a large, terraced stone window well where we could have plantings, and the window is a 4'x4' frosted window which opens. When you stand in the bathroom during the day there is a lot of natural light, and very little to make you feel that you are standing nearly 6' below grade.
In the main room, we put in a hardwood floor, which warms up the room physically and aesthetically. There wasn't any good ability to bring in natural light, so artificial lighting was critical. We put in 10 sealed low voltage MR16 recessed lights for general illumination, designer track lighting to highlight items on the wall and create a mood, and a recessed "laylight" or false skylight with dimmable fluorescent and a wood cover with a translucent panel made to look like a window cover. We also made a provision to put lighting in and above the bookshelf/cabinets. Finally, all of the lighting was controlled by a 6 zone Lutron Grafik Eye which allowed each of the 6 zones to be dimmed to create "scenes." The Grafik Eye also is controllable via infra-red remote control to tie in to the home theater.