Slate's The Big Money site takes up the question, noting that the recession might actually be good for the environment on balance. After all, the greenest shopping is not shopping at all. Next best is buying secondhand. Both of these, of course, are thrifty as well as green choices.

Energy-efficient choices like hybrid cars, CFL lightbulbs, EnergyStar appliances and insulation also save consumers money despite higher up-front costs, so demand for them should stay strong.

Where we've really seen a weakening, and are likely to see more, is in demand for products whose environmental claims are intangible and accompanied by hefty price premiums. This is especially true of organic foods which, the New York Times recently reported, have slowed from 20 percent annual sales growth in recent years to just 4 percent. Whole Foods Market, the flagship of sustainable groceries, is going through the toughest period in its history, with quarter-to-quarter net income slumping.

As an avid Whole Foods shopper myself, I find the objectives of sustainability, health, and good value often--but not always--converge. Vegetarian meal options are cheaper and better for the planet than meat (which we don't eat) or fish. Seasonal, local fruits and vegetables are simultaneously the cheapest, freshest, and lowest-carbon-footprint options. Literal "whole foods" such as bulk whole grains, dried spices, and canned beans are healthier and cheaper than processed, prepared meals and snacks. If I skip the organic raspberries flown in from Chile, I can splurge on the organic products that are most important to me from a health and ethical standpoint: eggs and milk.

Of course, I probably just described the lowest-profit-margin products in the entire store. How will you adapt your sustainable shopping habits to the recession?