Another trend that he says concerned him: the central role high-frequency firms play in the trading of exchange-traded funds.

WSJ: High-Speed Trading in the Spotlight

The exact cause of the Flash Crash of May 6, 2010 will most likely never be known, but most believe the use of high frequency trading as being a central culprit (no matter what the SEC might say).

FORBES: High Frequency Trading in Congress

Initial high-frequency data for September, though, point at a recovery in EM central bank demand for the common currency.

FORBES: EM Central Banks To Gobble Up Euros After Sharp Drop Against The Dollar