Over a million young people filled Cuatro Vientos to capacity and additional space had to be created for an overflow crowd of two hundred thousand pilgrims.
Pope Benedict XVI announced that the next World Youth Day will be in Rio de Janeiro, Brazil in 2013.
UPDATE [Aug 21]:
For complete texts of all of Our Holy Father's talks during WYD 2011, you can go to this link on the Vatican website:
Apostolic Journey to Madrid (Spain) on the occasion of the 26th World Youth Day
I just wish I would have known about this particular website sooner. It can sometimes be baffling trying to find the full text of the Pope's speeches online. Most news articles only provide summaries.