Adoration on Divine Mercy Sunday took place at Grotto as priests heard confessions until the last was heard. Adoration ended with Fr. Perrone leading the Divine Mercy Chaplet at 3:00pm, followed by Benediction. See Photo Post 1 - Divine Mercy Sunday 2007Fr. Edward McNamara, whose answers are posted in the Liturgy section of Zenit, answers the question of what's so special about Divine Mercy Sunday.
This is an excellent, comprehensive article with brief and concise history. It talks about the plenary indulgences and iterates the need for priests to be generous with confession time, and to lead the faithful in prayers.
Go read Fr. McNamara's response on Zenit...
The response names two documents related to Divine Mercy, found below.
Dives in Misericordia (Encyclical - Pope John Paul II)
Misericors et Miserator (May 5, 2000 Decree)