I am, this is a great question!

> How is that different?

What it means is that working on Dart is my job. It's a great job, and I love it. Like other good jobs, I get lots of both extrinsic and intrinsic reward from it. (In fact, a curious facet of being at Google is that the intrinsic rewards of being at the company feel like they overshadow the extrinsic ones. I'm constantly in this "and you pay me too?!" fugue of astonishment.)

But it also means that working on Dart is work. I do some extra-curricular activities related to it: I've spoken at a couple of conferences. But even then, I'm getting time off from work for free to go there, so in some sense I'm still being compensated.

I spend time answering questions about Dart online outside of work hours, but that's because, through some Hermione-like mental affliction, I will spend time answering questions about anything I know (and several things I don't).

But, aside from that, I actually don't do much of anything Dart-related when I get off work. Dart is what I do 40 hours a week. It's a happy 40 hours, but when I go home, I stop working on it and stop thinking about it.

Would I hack on it until the wee hours if I wasn't getting paid to do it while the sun was up? I don't know.