As an example,
most pollsters' samplings are NOT reaching (on a representative basis,
of course) the millions of Americans who in recent months have been
flooding voter registration offices in most states.

Guess who else isn't being polled?

Generation X, and those slightly younger but well into voting age.

Most of us over-40 fossils have a hard wired telephone. We're listed in phone
books. Because it's been so long since we've had to learn anything new, a lot
of us get lazy and fall for the slickest campaign pitch at election time. More
of us are Republicans. We see our lives as more than half over, and feel that's
it is more important to feather our own pre-retirement nests than to worry
wheter somebody else has any feathers. Because we have hard wired telephones,
we're the group called by the surveyors.

My 31-year old son *just* put in a hard wired phone and appeared in the phone
book. Up until now, he has used his cell phone for all purposes. My 27-year old
daughter uses her cell phone almost non-stop, would have no use for a
land-line, and doesn't appear in a phone book anywhere.

In summary, one of the basic assumptions upon which polls have been
traditionally based is that "almost everybody has a phone and is listed in the
phone book".
That was never true, but it is far less true today than it was only a few years
ago.