Speaking as an end user (but one who started writing code in the 1970s and spent his career in tech):
Pinterest managed to throw up a wall which prevented me seeing a picture my wife had linked. The signup process took too long, required me to select interests I did and do not have, and resulted in email spam. I will never visit the site again.
There are sites which have literally prevented me from paying, either because the signup-required-to-check-out process was broken with both Chrome and IE on Windows 7 (I think this occurring a second time should disqualify founders from ever getting money from a VC again), or because they thought my email had an account, but the password recovery didn’t work. Being able to accept order and payment from a customer is lifeblood, people. Act like it. On this note, if a site puts up a registration wall, and it does not work for any reason, I will leave the site and never return. No excuses, no second chances.
I really respect the NY Times approach, where it lets me see 10 articles a month, mentioning at roughly every other one how many of the 10 I’ve seen, but offering me an easy way to sub without interfering with seeing the content. Applying that approach to the register-wall would be best in class.
…and yes, I’m active on LinkedIn, somewhat active but only professionally on Twitter, and have a bare minimum Facebook account because some other context demanded it.