I did a quick websearch. Here is one guys trading system that does (easily) 100 trades per second on a 400Mhz machine 3 years ago.

video here : http://vimeo.com/18232653

code here : https://code.google.com/p/emte-trading/

In fact, I think it would actually be difficult to write a trading / matching engine that performed as slowly as mtgox. Seriously.