From my understanding of this, HFT basically makes it impossible for a non-HFT trader to buy at anything but his maximum buying price and to sell at anything but his lowest selling price. This seems like it would significantly undermine the profitability of the market for non-HFT traders.
HFT makes things very bad for day traders. It makes things marginally better for people who want to take or sell a long-term position. It doesn't change limit orders.
