2011: High-Frequency Trading makes up 53% of Wall Street Trading
Larry Tabb, President of the Tabb Group market research firm, says that 53% of all the buying and selling in US stock markets is automated through computer programmed trading. This figure is up from 2005, when it only made up 21% of the trading.
[Source: http://money.cnn.com/2011/08/12/markets/high_frequency_trading/index.htm]