I'm pretty sure it all comes from advertising.

Quote from the article:

Yet somehow we made it into 2009, and things began to look up. Long plagued by an inability to attract mainstream advertising, I partnered with an individual who took over representing 4chan's ad inventory, and for the first time in years the site began to break even.

Much of it Adult, too, since it is, well, 4chan.

4chan is not only /b/ and porn, there are surprisingly good SFW boards too. Well, maybe "SFW" is pushing it a bit, since the tone is still 4-chaney, but then look around the technology, cooking, or traditionnal games boards: you'll be surprised.

Oh, I'm well aware of that. /b/ is (arguably) the worst part of 4chan. 4chan has much more than porn, but it also has a lot of porn.

The world wide web has much more than porn, but it also has a lot of porn.

This was also true of Usenet.

/sp/ is honestly one of the funniest places on the internet.

i would say government at a guess

The site owner recently revealed he pushes 3500000 GB per month. My lowball estimate puts that at roughly $77,000 per month, just under a million dollars per year to keep the site running. There are no ads on /b/, which is the main board, representing I'd guess 95% of the entire site's traffic.

That, combined with the plausibility of the following, leads me to believe he receives massive government subsidies:

http://i.imgur.com/Dyo66.jpg

According to http://content.4chan.org/tmp/extensions.html they did 1.65 only petabytes for the month of June 2012, so where are you getting your 3.5 PB number from?

Additionally, https://www.cloudflare.com/plans seem to suggest the bulk of that costs an unbelievably low $3k/month.

I think $77k might be overshooting the mark a bit.

I once ran a site that pushed about 40TB a month (about 1% of 4chan) and it cost me $100/month to run. If you extrapolate that figure out (ignoring the fact that bandwidth gets cheaper the more you use), 4chan could cost as little as $10k a month to run.

If the allegations in the screenshot you posted are true (tl;dr: since 2008, the /b/ board is run by law enforcement as a sting operation), several prosecutions would have already run their course in the four years since the alleged start of the sting operation. Court decisions being open and including the details of the sting, we would have heard about it, wouldn't we? I think the press would have had a field day with that.