Oracle Text

Switch target creature's power and toughness until end of turn.

Card Rulings

11/1/2005 Note that the wording “Effects that alter the creature’s power alter its toughness instead, and vice versa, this turn” has been removed.
4/15/2013 Effects that switch power and toughness apply after all other effects that change power and/or toughness, regardless of which effect was created first.
4/15/2013 Switching a creature’s power and toughness twice (or any even number of times) effectively returns the creature to the power and toughness it had before any switches.