A lot of "compostable" plastic isn't compostable, at least not under the circumstances that most people consider to be composting... e.g. you can't put it in your backyard scrap pile and expect it to be gone in a few months. It'll still be there years later. One industry rep told me that they estimate their products take 30 years to completely breakdown and that's under perfectly ideal conditions -- bury it in a landfill with no oxygen, who knows how long it'll take. I guess that's better than 1,000 years... but still, it's basically another industry lie.