I went into my (very non-grub) Mollie Stone’s over the weekend and as my purchase was loaded into its plastic bag (without any hint of the old “Paper or Plastic?” option), I asked when they’d be transitioning to paper bags. The checker gave me a date in late November 2007.
My Google skills must suck as I can’t find much other information on when major grocery chains are supposed to uphold the ban. But I did find an interesting article at Sam Spade’s San Francisco. He makes a few observations about Safeway (boo hiss, it plays the role of corporate meanie in this post), and other grocery stores. If what he says is valid, why not take an extra moment to ask for paper (or use a bag?):

