This is one of the main reasons i detest pinterest. Lately they have changed, so that you can see small amount of the content, before annoying you with the login screen.
Ditto for Quora. I see interesting content, but they annoy me so much with their accounts (even when I'm just reading) that I never spend much time there. Don-t worry, I will create an account when I have something to say, but until then just let me be.