Well to be brutally truthful the plasmas will have a great deal of glare. Here are a couple of photos of my S1 Panasonic to explain it better:
That is me sitting on my couch and the light in the room is supplied by a full length door window to the left of my entertainment center. There is not enough light in the room to read by.
Just to show the screen with a dark scene picture on it as you can see the glare is still very noticeable. Now on sports programming where the screen is brightly lit, there is no noticeable glare at all.
Now light walls won’t necessarily be bothersome unless in the reflections there is a dark contrasting area as well such as the picture frames in the above examples. That’s when it gets objectionable for me. If the reflection was just a white wall, it would only deteriorate the super black levels, but not cause you to be seeing something in the reflection. It may be possible for you to tilt a reflective TV where it looks good during the brightly lit times, but still have the superior blacks and picture in the dark. Here is an example of a G20 with a couple of bright reflections to illustrate the issue of the problem with contrasting reflections. Those bright areas would show up in any dark scene just as they do with a totally black screen.
Thanks to soderholmd for the above photo who posted it on highdefforum.com of his G20.
Now going to an LCD is not necessarily going to get you a glare free screen because most of the brands have a reflective screen these days. My daughter has a Sharp LED backlit LCD and it has about the same glare as my Panny plasma. You have to shop around for a glare free HDTV that also has a good picture.
So if you are going to watch in a brightly lit room you can expect some glare. On the other hand in the dark you can not beat the picture of a plasma with any LCD.