[FireBeyond]

"To a certain degree"... Not so much...

So I, as a Content Creator, have to a) be mindful of, and b) take action to opt out of 1) Pinterest, 2) any other of a potentially large number of sites / applications, purely in order to ensure said sites don't claim commercial rights to and derive income from my work and effort?

Not the way it works, or should work, say I.

[icebraining]

You can send a DMCA takedown request if you see that someone is misusing your content. What exactly do you propose? Eliminate any website with user submitted content? I mean, what if someone posts a work to Hacker News without permission, should YCombinator be held liable?