One of the most frequent topics when sustainability wonks get together, in person or online, is "greenwashing". Greenwashing -- the design and production of products which can be marketed as contributing to sustainability, but which in practice change little or nothing for the better -- is a frequent practice and an even more frequent accusation. Would switching to product X, or service Y, or process Z really reduce greenhouse gas emissions? Are the benefits real? Is the approach well-intentioned but fundamentally flawed?