If Facebook is commercial, does that make it legal for you to post a CC-NC-BY document you didn't write as a Facebook Note? If it's legal for you to post it, is it also legal for Facebook to display it, thus drawing people into their site to view advertising? What if I set up a paid-subscription-only Facebook clone called Flone and you post it on Flone, so that you have to pay Flone to see the Note? Does it matter if Flone charges per pageview instead of per month? Does it matter if Flone charges more for certain pageviews? When Verizon sells you a data connection, are they in some way different from our hypothetical Flone?

Good point