Surprisingly, their "post kill-rate", apparently a measure of spam, dropped by a factor of two as well.
From Blake's post:
Back on December 12th, we released a site redesign that included user forums on each of our news pages .... One month after launch, we were still under 200 posts a day.If the intent is to control spam, requiring registration may do more harm than good.
Could we take the registration down? Of course the volume would go up, but what would happen to the quality of the posts? ... Was this going to double or triple the amount of spam and profanity we needed to parse through? Would an army of trolls invade and set up a siege?
Since removing registration, our volume has exploded and just this morning we just passed a quarter-of-a-million aggregate posts on our system.
And the quality of posts? To our surprise, our post kill-rate has actually dropped -- hovering below 2%. This is less than half of the number incurred when registration was in place.
We think it's the "Ni-chan paradox" .... Registration keeps out good posters ... Registration lets in bad posters ... Registration attracts trolls ... Anonymity counters vanity.
Slashdot is another great example. Slashdot allows anonymous posts in their forums. To control spam and surface good posts, Slashdot relies on user moderation.
It might be possible to extend this lesson to other areas. For example, many newspapers require registration, repelling many visitors.
Mandatory registration at newspapers has been a heated topic of debate. Here is a sample of some of it:       .
Some newspapers, most recently the Houston Chronicle and Toronto Star, decided to eliminate mandatory registration, citing their desire to improve usability and increase traffic as the major factors in their decision.
Eliminating registration does not mean giving up on targeting advertising and content. Findory, for example, does not require registration, but still helps readers find relevant content and advertising by carefully paying attention to which news stories interested each person.