In 1987, John Cage composed a musical piece titled Organ²/ASLSP (As SLow aS Possible), with instruction that it should be played as slow as possible.
But how slow? In a 1997 conference for organists, musicians and philosophers came up with a project to play Cage's piece over 639 years! They got started in 2001, and although that was quite a while ago, you haven't missed much: they've only played 5 notes so far!
http://www.john-cage.halberstadt.de/new/index.php?seite=cdundtoene&l=e (the note is playing, so turn down your speakers) | Wikipedia entries on John Cage, As Slow As Possible - Thanks kaiserandi!