Wow. That is nuts. The thing is, for technical jobs like the ones folks at Hacker News tend to have, I find almost no difference in my output between 30 and 40

Wow. That is nuts. The thing is, for technical jobs like the ones folks at Hacker News tend to have, I find almost no difference in my output between 30 and 40 hour weeks. 30 hours / week I'm more mentally / physically refreshed and better able to problem-solve, so I get my work done faster. The only advantage to a full-time schedule is that it's easier to coordinate / follow-up with other people.