From Timothy Lavin (The Atlantic, August 2010):
By some estimates, algorithms now trigger 70 percent of all trades in U.S. equities. The speed and volume of everyday trading have propelled the market into a new and esoteric dimension, and rendered traders in the pits largely obsolete. Average daily share volume on the New York Stock Exchange increased by 181 percent between 2005 and 2009, while the time required to execute a trade on its electronic systems dropped to 650 microseconds.
Over 2/3 of all trades are made by computers? Who is looking out for the buy-and-hold investor? Seems like all the benefits go to the speculators these days. More here.