Kiba, just google "Gold Manipulation High Frequency Trading" or "high frequency trading scam" to get some ideas.

I dont think that high frequency trading is a scam per-se, but it can turn into one quite easily if used by poweful people with certain goals in mind.

To repeat, if Bitcoin is used massively as a medium of exchange for services and products, then what happens in the currency exchange donsent matter anyways, with or without high frequency trading.

On the other hand, if Bitcoin is used for hoarding/saving/speculation only, and its price is set mainly in a few concentrated places (i.e. currency exchanges like MtGox), this can lead to easy manipulation of price by powerful people who can exert hidden control in this few markets. The main idea behind Bitcoin is distributed economic power to the people, not a few crooks in the dark setting prices and controling the fate of the currency.

By the way, I dont condemn saving/hoarding bitcoins. This is a very valuable quality of sound money, to be able to serve as a store of value. I am only predicting the failure of Bitcoin if we cannot make it a popular medium of exchange for goods and services.