I don't know how surfn does it, but I suspect he's almost 100 years old and submitted his first freesite the same day Al Gore invented the internet.
What I'm trying to say is that traffic like that probably doesn't build up over night. After less than a year in the business I'm sending roughly 30k to sponsors/month. Not a hell of a lot, but at least it's an upward trend.
There's also a snowball effect as your portofolio of freesites grows. Once you have a couple 1000 out there with PR i suspect SE traffic becomes significant. Only today I got about 700 hits from Google/Yahoo/MSN absolutely for free.