Powder Person Here
I use powder because - in spite of the politically correct misrepresentations in many ads today - liquids are not good for this planet.
They incorporate two major problems:
1) Their bottles are made of petrochemicals, and please don't talk to me about recycling, because the dirty little secret of recycling is that not all that much actually does get recycled. The idea of recycling works far better as a mechanism for reducing consumer guilt than it does to reduce waste.
2) They contain water, which is heavy and therefore costly to ship, in both the ecological and financial senses. Newer "Ultra" products contain less water than former products, but they still contain water, which means they weigh more than powders.
Give me a powder with almost no water content, shipped and sold in a biodegradable cardboard box made with renewable resources, every time. If our detergent manufacturers were actually as serious about ecology as their ads would have you believe, they would be pushing powders, not liquids.