Treasury bonds (of the same date and maturity) are completely fungible. One is exactly the same as the other. It doesn't matter who the Fed buys it from in the long term: there will be fewer outstanding Treasury bonds and more outstanding US dollars, and the price of a Treasury bond will be higher. If Goldman Sachs owns US treasury bonds, they will benefit from quantitative easing one way or another, simply because the value of those bonds goes up when the Fed is willing to buy them at a good price.
In the short term, banks might do things with money (like make loans and perform other investment activity) a little faster than the Treasury. (The Treasury might skip or reduce the size of future bond sales.) There is also the opportunity for a tiny amount of arbitrage between the market price of a bond and the price the Fed is willing to pay, but everyone with a big chunk of bonds is able to compete for that little bit of profit (which is why these things are called open market operations) so it's not really all that hot.
Really, people! There are far more legitimate criticisms of QE2 than Goldman Sachs participating in the treasury auction process! For starters, consider criticisms of the effects of the policy.