FYI: This isn't an HFT bot but is a decent, recent Python + ncurses trading client framework for Bitcoin on MtGox. http://prof7bit.github.io/goxtool/

Even if you aren't interested in Bitcoin, it might be useful as a real-ish and cheap place to test with low barriers to entry. I've found that backtesting on historical data is usually not realistic enough since most people fail to consider liquidity.

I'm interested because I like to trade, would like to learn more, and I have had some small success. But I have trouble sticking to my plan. I let emotion get the best of me and wind up losing my gains.