In responce to the lack of curtains between first and business class, all US carriers were required by the end of June 2003 to remove cabin dividing curtains in the intrest of security. This allows the flight attendats to have an unobstructed view down the aisle and it allows any sky marshalls(sp?) to have a view down the entire aircraft.

Some UA flight attendants elect to make an announcement regarding the open curtains and they request that passengers utilize the restrooms within their own cabin. Not everyone listens.