I've made a positive and not insignificant (percent-wise) profit day-trading ~10 times per day on volatile market days. I'm not sure that HF trading would net me any more though. My MtGox client could theoretically support it, but I'm really not the person to write an AI for trading...
It doesn't have to be complex or complicated. Can be something like: If bitcoins drop below 10$/btc then buy 3 coins. Place sell order at 15$/btc for 3 coins. If sell order successful then place buy order for 10$/btc for 3 coins, rinse and repeat. If the market is volatile between 8-17$/btc bouncing up and down then this could be profitable. If you buy and the price of btc drops to 7-8 then the software just stands idle until the coins are sold at 15$. You could also make the buy/sell orders for 1$ spreads or whatever amount you want. The idea is to buy low and sell high. If that fails then its basically buy and hold long term until price recovery.
Of course there is always the risk of loss in such a situation, I am just thinking of this as a, "for fun" project. Maybe writing a simple script, dropping $500 into the mtgox account. Configure the script and let it run for a couple days. If I lose the money, then it will be fun. If I make money then great.
The problem is sometimes I just can't react fast enough only a computer can.
I don't understand what you mean by this. You would write the trade bot so it pulls btc price data from mtgox and then write triggers based on that price. The triggers would send buy/sell orders. Once one of those buy/sell orders is filled then it would place a different order. All the orders will be placed in such a fashion that you benefit from the order being executed.