So, you got your Instructable all posted and sent it to all your friends, and somebody comes back with, "Hey, I want to print a PDF but it says I have to pay."
"Hmm," you say, "I thought I specified Non-Commercial in my Creative Commons License. Let me check on that."
And so the journey begins.
Log out of Instructables and find your own Instructable. Click on the "more info" link.
Step 1: Download that PDF
Your friend must be crazy ... Instructables doesn't violate the Creative Commons licensing. There's not even mention in their Terms of Service [yet as of 2009-Aug-17] about a separate license between you and Instructables so they can charge for your work.
So while you're logged-out (as if you're an anonymous Interweb lurker), click on that PDF link.
What's this? I need to have a "Pro" membership to download PDF's? Okay ... and it's a modest (but not Non-Commercial) expense. Hmm ...
Update 2009-Aug-19: I should have read closer. In 7(d) it says, "you grant Instructables the world-wide, royalty free, perpetual, irrevocable, non-exclusive and fully sublicensable license to use, distribute, reproduce, modify, adapt, publish, publicly perform and publicly display such Content solely for the purposes of providing and promoting Instructables." It's the "royalty-free" thing that implies they can collect money but they're under no obligation to pay you part of it.