Mt. Gox I believe has a flat percentage fee on all trades so someone can make as many micro trades as they want and still pay the same fee as one large trade.
It's pretty easy to solve by charging users who make over a certain limit of micro trades. I wonder why they haven't done this?
This actually seems like a large flaw in their fee structure. Every traditional online brokerage/trading service that I have looked at in the past has used a flat fee. This incentives individuals to reduce their number of transactions in order to limit the overall fee's paid.
It's pretty easy to solve by charging users who make over a certain limit of micro trades. I wonder why they haven't done this?