As I see it, the product of the computations is a "supersignature" on the block chain.  A block solution carries the hashing community's endorsement of the transaction history and attests to its completeness, thus protecting receivers against double spends.

I am thinking of replacing the reply at https://en.bitcoin.it/wiki/Myths#Bitcoin_mining_is_a_waste_of_energy_and_harmful_for_ecology with the following text.  I would appreciate expert comment:

The electricity spent in hashing is not wasted. It creates a product of value to the Bitcoin economy. The product is a supersignature on the complete list of transactions to date (the Block chain). This supersignature attesting to the chain's completeness is Bitcoin's defense against double spending.

Many sources of energy vary in their availability in ways that do not match the variations in demand. The law of supply and demand should require Bitcoin to soak up a lot of energy that is currently "wasted" before it makes a big dent in the otherwise usable energy supply. [Perhaps cite estimates of the break-even point for mining profitability that imply near-zero-cost electricity.]

Cheers,
John