I know some of the upper tier Sony widescreen projections (XBR?) have an anti-reflective coating on the front. Don't know how well they work. Might just be a glare reducer, not necessarily a cure for reflections.

Remember, with projection screens, you have two separate issues with ambient light:

1. The overal ambient light coloring the screen itself, which is usually a shade of gray. The brighter the ambient light, the brighter the base color of the screen. For instance, the screen is never actually black, you just get the illusion of blackness because all the other colors are very bright next to the dark areas. The brighter the ambient light in the room, the less black the screen will appear and the worse the picture will look. The anti-reflective coating on the protective glass covering a rear-projector screen has nothing to do with this.

2. Mirror reflections of the objects in the room on the face of the protective glass. For instance, if it is bright in the room, then you will be able to see yourself sitting on the couch, mirrored in the glass. A good anti-reflective coating can help with this. But it doesn't solve the other problem.