Most of the conductors with whom I've talked about this tell me that they
make no specific effort to memorize scores.  It's just that once they've
worked with a piece enough they find themselves referring less and less
to the score while they're conducting it and eventually find turning
pages and so on to be more of a distraction than it's worth.  I'm not
sure whether the public is particularly impressed when a conductor goes
scoreless.  I know it can make an orchestra nervous.  It would be a rare
orchestral musician who has never had to cover for a conductor's memory
lapses and acts of fakery.

Richard, who invites you to visit his music, outdoors and other WWW sites
at: http://infoweb.magi.com/~richard/