A few years back there was a HFT guy that posted a few blog entries describing (and defending through it's liquidity creating properties, IIRC) HFT setups. I don't have the article, but I imagine both tptacek and patio11 (and a slew of others) have a good idea of what I'm talking about, and may be able to dig up a link. You might find it interesting (if it's not already entirely covered by Flash Boys, which I haven't read).