http://www.mymoneyblog.com/archives/2008/12/historical-distribution-of-annual-us-market-returns-from-1825-present-how-bad-was-2008.html

based on the diagram in this post, 2008 is 'once-maybe-twice-in-a-lifetime' type of a year, as far as investing is concerned. interesting, huh? wonder where 2009 will end up...