The execution job is more and more computer / algo driven both in Prop desk and hedge funds.
In 2006 at the London Stock Exchange, over 40% of all orders were entered by algo traders, with 60% predicted for 2007. American markets and equity markets generally have a higher proportion of algo trades than other markets, and estimates for 2008 range as high as an 80% proportion in some markets.
The US market's big swing in the past 2 days is also a good indication of computer algo driven trading. Big swing, light volume...Just a show.