An extremely eco-conscious friend of mine who lives in the UK was telling me that often, even when there is a choice - such as paying a few pennies extra for a biodegradable compostable plastic package in which her organic fair trade carrots come in ;p the supermarket will often go and put an absolutely non degradable metal sticker on it that doesn't come off or some such thing that essentially cancels out the entire concept with one thoughtless gesture.
Its almost as though sustainable design needs to look at the big picture holistically or the entire industrial ecosystem needs to be designed from this point of view, in order to ensure that the time, effort and expense of using a compostable plastic package is not cancelled out by one simple act.