Our favourite Bethesda PR guy, Pete Hines, has been interviewed by PCGZine and had this to say:
PCG: Players can expect different
outcomes if they thread a neutral path in Fallout 3. Will you be
tripping conservative players up with disproportionately good/evil
outcomes if they try to mind their own business?
Hines: Yes, whether your karma is good, evil, or
neutral, you’ll experience different things. At one point in the game,
if you’re evil, the good guys try to kill you, or if you’re good the
evil guys try to kill you. If you’re neutral, everybody leaves you
alone. So there are drawbacks and advantages for neutral just as there
are for good and evil players, and we’ve spend a lot of time working on
the gameplay options and outcomes for that “grey” area in between as
sometimes the most interesting choices can be found there.