It does look good on the Watch. But that doesn't automatically mean it would be a good choice for other uses. In my subjective opinion it looks pretty bad as OS X system font. Take a look: http://9to5mac.com/2014/11/19/how-to-use-the-apple-watch-fon...

We're operating off of rumors and a font hack that uses a font designed for hi-fidelity mockups of Apple Watch apps. I'm going to wait and see what Apple releases.

The statement that it's "like a Starship Enterprise" in that screenshot hit on exactly how the system-font-ization looks to me. It feels clinical somehow. It's definitely not a neutral statement—which is usually what people presume a system font should be.

Instead, it feels like something I'd expect to come with a redesign to the OS itself to make it all a bit more brutalist-feeling; maybe something that relies on Gestalt windows-menus-and-pointers less, and a narrative interface like Siri more. A HAL9000 chat-transcript.

Thanks for the link to that page, which contains a large image of a screenshot using San Francisco as the system font.

To me, it looks really great as a system font.

The reason is that it is legible. That legibility comes thru the junk on my glasses and the fact that my prescription is out of date so things are just slightly blurry. Yes, I need new glasses.

But that's a proxy for people who don't see as well. Apple's serving everybody. And not all of us can see so good.

There's an argument that this line of thinking will take Apple down the path of mediocrity-- lowest common denominator and all that. But hopefully it's only an option and they continue to use the "Best" font (of which I'm not the best judge) for the system.

And then make San Francisco an option as a system font in accessibility.

No, I'm unhappy with its style, which is clunky and clumsy.