The typophiles here will surely yell at me for getting the terminology wrong, but my experience is that fonts are heavier on OS X and whenever I see a site with whisper-thin text like the above I suspect it was tested on OS X only.
Edit: removing the font-weight CSS attribute makes the page legible. The issue is that you specified a font-weight under 400 ("normal"), and different font engines snap in different ways.
But I bet that the text you're looking at right now on HN is easier to read than the screenshot. Now consider that people might have dense screens, or sit further away from the screen than you do, or have poor eyesight.
Nah, it’s still too light on OS X with Safari. And on a Retina screen, no less. If this would work anywhere, it would work on that combination of screen, OS and browser. But no, it does not.
I can read it comfortably if I lean in, but I'd rather not. The text here on HN is smaller than your site, and it's perfectly readable from my normal position.
