Check the online Maya 2009 Help file to see what's new in more details.
It is not official available but you can read from this link:
Code:
http://download.autodesk.com/us/maya/2009help/index.html
It contains some videos for the new multi-render passes also:
Code:
http://download.autodesk.com/us/maya/2009help/movies/RenderPasses_Part1.html
http://download.autodesk.com/us/maya/2009help/movies/RenderPasses_Edited_2d.html
http://download.autodesk.com/us/maya/2009help/movies/RenderPasses_PartIII.html