Actually, according to the following sources, the content is written to disk _before_ entering sleep. This can be done very quickly because most of the data is already in swap file.

http://support.apple.com/kb/HT1757?viewlocale=en_US http://www.macworld.com/article/53460/2006/10/safesleep.html http://moishelettvin.blogspot.com/2006/11/windows-shutdown-c...