It does work for all accounts, I just signed up for my preferred charity, Book Industry Charitable Foundation. Go see if your favorite charity is listed and if they aren't please make sure they know about this program.
As an FYI, if you have an Amazon account, Amazon just released a new program called Amazon Smile that costs NOTHING to you. You can pick OPS (Oceanic Preservation Society) or just about any other charity/organization of your choice and Amazon will donate .5% of your purchase cost to the charity every time you buy an eligible product.
I already buy most of my things from Amazon, so yay! Glad to know a small portion of the cost will be going to an organization that I really love.
EDIT: Details of the program can be found by clicking here. This MAY work for all Amazon members, but it's not very clear.
EDIT 2: It seems to work for ALL members, not just those with Amazon Prime.