At Mt Gox YOU PAY a commission of between 0.25% and 0.60% of the value of your trade ON ALL TRADES.
They PAY YOU 0.1% of the value of your trade for trades that add liquidity to the order book.
For orders that take liquidity from the order book you pay a commission 0.4%.
But if your trading style is to let the price come to you, this could be huge!
If enough of us traders move over there, we can save a ton of money in commissions.
I've already got orders on www.BitFloor.com
Come and join me.
P.S. They also support Dwolla!