Text (6th+errata): Artifacts, creatures, and lands your opponents control enter the battlefield tapped. [Oracle 2009/07/08]
Cards enter play tapped. They do not come into play untapped and then immediately tap, therefore they do not trigger any effects due to tapping. [D'Angelo 1998/02/03]
It affects all opponents. [D'Angelo 1999/05/01]
It applies to cards and tokens that are put into play by an effect, as well as ones that are played from the player's hand. [D'Angelo 1999/07/03]
It applies to cards and tokens put into play under your control by an opponent's spell or ability. For example, with Flicker. [D'Angelo 1999/07/26]
Does not affect cards that phase in. [Duelist Magazine #19, Page 30]
Note - In Fifth Edition (and before) it affected just one opponent.
