Intersango is trying, but BitFloor has the right formula.
At Intersango liquidity takers PAY 0.95% and liquidity providers PAY 0.35%.
At BitFloor liquidity takers PAY 0.4% and liquidity providers RECEIVE 0.1%
I trade BTC/USD at Mt Gox, Crypto X Change, Intersango, CampBX and BitFloor. Each one has their advantages, but when it comes to commission structure, BitFloor has shown the way.