If they haven't already mastered the art of separating recyclables from the rest of the trash, most people will soon get the hang of it -- particularly with the prospect of inspectors peering in their garbage cans to double-check their skills.

But once the paper, glass and cans are tucked into the right bins and the truck comes and hauls it away -- what then?

Well, then the truck takes the paper and glass and aluminum and steel to a collection center, where the waste is sorted and bundled, to be returned to its respective producers to be reused, thus saving money and energy and reducing the environmental effects of incinerating or dumping the material in a landfill.

We hope.

Recycling has so much appeal to so many people in so many ways, not the least of which being the seeming opportunity to do well by doing good. By reusing materials instead of just throwing them away, by avoiding the production of new material from scratch, by keeping waste out of landfills, and by paying for the collection service through the sale of recycled material, it just feels like the right thing to do.

But is a "feeling" the same thing as actually making financial or environmental sense?

That question was a theme in one of the better books of 2005, Elizabeth Royte's "Garbage Land." Royte, a New York resident, was curious about what happened to her trash once it left the curb, so she began tracking it -- to the collection station, to the recyclers and to landfills. She talked to the true believers and skeptics.

In doing so, she unearthed the great debate over recycling.

"Even when residents doubted the efficacy of recycling ... they continued to go through the motions," Royte writes. "Across the nation, more people recycle than vote. Recycling is a religion for some, and setting out bottles, cans and newspapers is redemptive -- a spiritual balm for our collective solid-waste guilt. We are powerless to replenish the ocean's fish stocks, to scour the chemicals from our rivers, to combat rising atmospheric temperatures, to halt the spread of exotic weeds and the global decline in biodiversity, but we can, by God, continue to sort out garbage, to make our offerings at the curb."

Complex, because there actually are so many factors that go into it -- the comparative costs for collecting, hauling, sorting and processing recyclable material vs. using new sources of material vs. just hauling all of the stuff to a landfill (or burning it), not to mention the environmental and energy-consumption pluses and minuses for recycling vs. disposal (on which, as Royte's book notes, there's considerable disagreement).

Making the calculations even more challenging is that the components don't stay the same. In 2006, demand for recycled materials is strong and prices are up for commodities such as paper, aluminum and plastics (glass, by contrast, has been sluggish).

A stronger national economy is boosting consumption of recycled materials. So is greater use, compelled by law, regulation or an interest in burnishing a company's environmental image. Rising prices for oil and natural gas, as a feedstock or fuel, make recyclables (which often require less energy to process) more attractive. Preston Horne-Brine, regional procurement manager for Marathon Recovery, says the recycled plastics market has been boosted by Hurricane Katrina knocking out production capacity.

The increased demand is coming not just from domestic customers but from overseas markets -- China, not surprisingly, being a huge influence. When recycling markets were launched in the early 1990s, "The Pacific Rim and China weren't markets for this material," says Jerry Hardebeck, director of public sector services for Waste Management Inc. "They are today."

So strong are the markets for some commodities such as aluminum and certain grades of paper (newsprint and cardboard), Hardebeck says, that a curbside collection program focusing on those materials "could come very close to recovering" its costs.

Which adds still more interesting questions to the debate. Do we collect just those commodities for which there's a strong market? Collect them all and let the strong "subsidize" the weak? Should recycling programs be expected to break even? Is close good enough? How close? And what happens if prices for certain recyclables swoon?

The calculations aren't going to get any easier. More demand (spurred by market forces or law) will drive up prices, but that in turn might encourage more collection (more supply means lower prices) or encourage customers to go back to raw materials. Increased efficiency in collecting and processing recyclables could help cut costs. Landfills may prove more expensive to build, maintain and clean up. Then again, there could be unforeseen forces (such as product substitution) that clobber the markets for one or more of those commodities.

The accommodation that many people may reach is this: A program that recovers at least some of its costs (which is more than we expect from most government ventures) and provides at least the semblance of environmental remediation is enough to justify a "feel good" premium that we pay.

Of course, if it so happens that recycling programs eventually do pay for themselves, that would be a nice feeling to have, too.