Reasons you may not have thought of to buy shade coffee:

1. It often tastes better. Why? TYPICA-ly, the coffee varieties present in shade coffee farms are the older ones (bourbon, typica, maragogype), which produce fewer beans, more slowly, and with higher levels of sugars. This has been noticed by many of us in our cup tests for years, and was shown to be measurable scientifically by French scientists working with Anacafe in Guatemala.
2. Lemurs, and monkeys, and ants (Oh My): Bird lovers concentrate on songbird migration as the main reason to save the forest overstory, but a great number of other endangered creatures increasingly rely on these special places to survive--everything from rare frogs, to ants, monkeys, "precious wood" types of trees, and myriad plant, animal and insect varieties (sorry, no bears that I am aware of). Which leads to...
3. The Noah's Ark effect: Much of Puerto Rico's native bird and plant species had been drastically reduced by the first quarter of the twentieth century, as populations encroached upon the island's last pristine spaces. When coffee was abandoned (due to low prices...sound familiar?) the shade farms turned out to be important biospheres that allowed the native flora and fauna to survive, and it has spread back out naturally as more stringent environmental laws were enacted. This scenario is now present in other places as well. For example, in El Salvador, where 98% or more of the original forests have been lost, much of the biodiversity that is left exists in harmony with shade coffee agronomy. (The idea of a biological corridor extending from Mexico to the Amazon, proposed last year during an SCAA speech by El Salvador's Minister of the Environment and several other Latin American scientists, depends of coffee farms as an essential part of the plan.)
4. You'd like to see the snows of Kilimanjaro before they are gone. Scientists tell us that global warming is having not-so-subtle impacts even laymen can see. One of these is the loss of glaciers in places like Peru and Switzerland. Guess where we are likely to see it first? Africa, actually. Center of the Rift valley, specifically...where the only glacier on the continent sits in Northern Tanzania. Best guesses currently have the last of the ice disappearing within the lifetime of folks born after, say 1970. One of the few ways we know of slowing this is with carbon sequestration, and in our industry, the only significant thing we can do is to save/plant shade trees. (Coffee trees, alas, are nearly useless in the equation, but the shade trees can be meaningfully helpful.)
5. Human health and welfare. Unlike technified farms, which are plied with large amounts of chemical inputs--and increasingly tended with mechanical equipment-- shade coffee inevitably requires hand tending, and uses far less (if any) in the way of petrochemicals. Of course, we will pay more for coffees that are grown in harmony with nature, and cared for by humans, but that's the nature of today's coffee industry. Decisions like this are part and parcel of running a company on a planet of six billion (and climbing...) and the need for jobs in the third world is already at the crisis point.