I just pinned a bunch of my own images today. Flickr, don't tell me what I can and can't do with content I created myself.
By using the full "all rights reserved/copyrighted" status, you’ve essentially told Flickr and any users viewing your photos that any use of that photo must go through you first.
What if I’m a professional photographer who doesn’t want my photos re-posted everywhere to, in essence, help Pinterest gain users make money? (Rhetorical, by the way; not a pro photographer and most of my photos are under the least restrictive CC-BY license. I personally think photographers could stand to get a lot more exposure via Pinterest.)
Any photographer or artist who really doesn't want their images shared should not make them available on the internet. Period. Given the capabilities of current computing platforms, there exists no method by which you can restrict redistribution.
Imitation is the sincerest form of flattery.
For example: There's no technical way I can prevent you from slandering me, short of preventing all of your speech. However if you do slander me, and I find out about it then I can take you to court.
The nopin setting just enforces a gentlemans agreement between Pinterest and the site in question. If the Pinterest user really wants to share that picture, all they have to do is copy the link and do it manually.
Flickr makes an effort to spell out to visitors the terms of your image's copyright (whatever they may be), as a photographer that's where their responsibility ends, and I'm ok with that. I do not expect Flickr to slap DRM on it on my behalf and go out of its way to prevent the inevitable.
If someone wants to throw my photos on imgur and share them without attribution, there's not a lick of anything I can do about it, Pinterest or otherwise. Flickr has done its due diligence informing users about the legalities of whatever use they have in mind, and that's fine.
Also, when I hit the Pinterest bookmarklet, I am logged into Flickr, and staring at one of its own pages. Flickr knows exactly who I am - the same logic that's locking out Pinterest could just as well check if I have permissions to share these images.