This year was the 33rd edition of the festival and it ran from Jun 28 through July 7.
They had 800+ concerts, 600+ activity/animation areas around the festival!
For general festival details and tips, visit this local page: Montreal Jazz Festival.
A few samples from the 2012 Montreal Jazz Festival, and the stage where they played [ site map ]:
Sidi Touré Les Soirées Jazzy stage
The Pitbull of Blues Band Les Soirées Blues stage
Bob Harrisson Les Soirées Blues stage
Danakil Groove stage
La Chiva Gantiva Les Tropiques stage
Lady Linn and her Magnificent Seven Les Soirées Jazzy stage
Besh O Drom Les Performances TD main stage (Clip 1)
Besh O Drom Les Performances TD main stage (Clip 2)
Chicha Libre Les Tropiques stage
Chromeo Event closing performance (Clip 1) Electronica rules!
Sideshows in the designated activity areas:
Acrobatics
Drums
Official video clips of most of the music shows: All Videos (though not sure how long they will keep the official site up).