I have liquidated my Goldman Sachs postion. I switched to crude oil and gold contracts for my commodity portfolio. The trouble with the Goldman Sachs Index is:
a) You can't buy long term contracts. They are available for only a few months forward. That is, in June, the farthest out contract you can buy is for August. If you believe there will be long term inflation in virtually all commodities, it does not make sense to place such a short term position.
b) The only decent liquidity is in the front month.
The upshot of this is that you have to roll over your position every month, which is stressful and can be hazarous to your balance. The oil and gold contracts are better for a small investor, who doesn't want to be day trading. They are very liquid. You can buy them years out if you prefer. And the contract size is smaller than the Goldman Sachs, so you are not putting as much of your capital in one contract.
But I liked the idea of the Goldman Sachs Index, it seemed to represent a reasonable cross section of the global economy.