Yeah, isn't it against google's policy to present different content to bots and to fleshy users?

That is their policy, but they don't appear to punish people who violate the "spirit" of it and many of these sites don't literally violate the rule.

In the case of pinterest (and quora), for example, the whole page you are looking for is there, it just gets obscured by an obnoxious overlay that makes it impossible for you to see/interact with it all from a browser unless you register.

I'm sure what the googlebot gets at the html/css/js level is the same thing the user gets. The difference being the bot doesn't care about the semi-transparent blocking overlay because the bot is just parsing text/images/links individually and not trying to interact with the page the way a human does.

Not anymore apparently, at least for the big players. I believe it is still the stated policy and you won't get away with it if you are small.

Pretty sure it is.

Reminds me of the amusingly named 'expertsexchange' site, and the stackoverflow copies. Google shoved them down the ranking pretty quickly. Shame they don't do that to pinterest.

I always read that "expert sex change" instead of "experts exchange" for some reason;

Favoring first match vs. longest match.

I never saw it that way, but you have now set me up to chuckle randomly at the memory all day. Thanks!

For the 'please register' overlays, you need an 'extension' called Kill sticky. It removes all html elements that are styled with 'position: fixed'

Here's the link: https://alisdair.mcdiarmid.org/kill-sticky-headers/