emmett: This is taken from http://senseis.xmp.net/?Komi :
"With the notable exception of the Oteai, almost all tournaments nowadays, both amateur and professional, use komi. But this has not always been so. In fact, komi was rarely used in professional tournaments before 1937, and its gradual introduction into professional play was not without controversy.

The usual komi in Japan was for some time 4.5 points (specified as 4 points with White winning jigo)[4], although even lower values were commonly used early on. In 1955 the Oza became the first tournament to adopt 5.5. Today the standard komi in Japan is 5.5 points, although the Nihon Ki-in decided to change to 6.5 in September 2002.[1] Korea also used to use 5.5, but is already in the process of switching to 6.5.[2]. The usual komi in China was formerly 5.5, but 7.5 is now standard.[3] The Ing rules also have a komi of 7.5, specified as 8 points with Black winning jigo. Western countries often used to follow Japanese practice in using a komi of 5.5 points, but tournaments with komi set at 6 or 6.5 are not uncommon. The New Zealand rules specify a komi of 7. The American Go Association changed komi from 5.5 to 7.5 in August 2004, effective 2005."