B) Half-Life 2 had used shaders in some areas, in future versions shaders will be much more wide-spread. You have to remember the extensive physics in the game did not give it the extra horsepower to per-pixel light the entire levels.
C) To make an successfull FPS game your going to need the entire levels per-pixel lit, or, make up for it in content(I mean physics, object littered levels ect.). The only way I can see a commercial FPS without per-pixel shaders for everything is very large outdoor areas. But if your starting your game now then it's smart to have that per-pixel lit as well.
D) You'll need shaders as an option in most other generes past the FPS.
E) Quake4 had low res-textures. The future will be per-pixel light with higher res textures, realtime shadows, ect. basically what's rendered with the help of the Sphere engine(minus the physics, A6 physics are not the quickest if you like stability, never tried Newton so cannot comment there).
In my game I decided not to go with per-pixel lighting for the full scene due to speed reasons. This is an outdoor kart racing game with very large racetracks. Karts contain A.I, weapons, ect. Currently I have a slew of options for graphics. In the shader department I've got bloom, multi-texturing, all the powerups, water, skies, vegetation, screens, set peices, and various weapon effects. The game also runs on low end computers due to the options(4 major graphics options). My nearly identical FFP effects run slower than their shader counterparts. Either way, shaders arn't toys, they really affect the lighting in your game and make everything more "dynamic". And they will change your art direction, so it's best to plan ahead and have all your options in place before you do the art.
