Another point about green jobs worth chewing on is that the question of whether they're a good idea depends on your assumptions about economics. If you believe, in accordance with standard economics, that economic growth is an unalloyed good and that maximizing productivity (labor productivity in particular) is key to raising living standards, then a green jobs agenda, which promotes labor-intensive projects, is not necessarily a good idea.
On the other hand, if you subscribe to various heterodox schools of economics, then green jobs becomes a more reasonable response: In ecological economics, for example, preventing natural resources from being depleted at an unsustainable rate means maximizing the productivity of natural resources relative to labor; an economy based around manufacturing and increasing consumption gives way to one based around maintenance and repair, but little growth, if at all. Similarly, many heterodox economists have argued that the returns to increased efficiency should come in the form of reduced working hours instead of more production. This would not only have the potential to increase employment, but could also reduce energy consumption and, by extension, carbon emissions.
Now, I'm skeptical of how useful such perspectives would be for the current debate about green jobs and a greener economy -- I doubt you'll see Herman Daly, say, in Barack Obama's company anytime soon. But as I said, it's worth contemplating.