Text (5th+errata): Each player shuffles the cards from his or her hand into his or her library, then draws that many cards. [Oracle 2007/02/01]
The number of cards you originally had is the number of cards in your hand when this spell is resolved, and not when it is played. In other words, if you start with 7 cards, cast Winds of Change, and then cast 5 other instants in the same stack, then you will get 1 new card and not 6 or 7. [Aahz 1994/09/06]
