It's the reason your site's fonts look so terrible in Chrome for Windows.
Nothing says built on a mac like jagged webfonts on Windows.
Edit:
Here's some more info on the issue, to (hopefully) be more useful:
"Using Web fonts in your design requires thorough testing on as many different browsers and platforms as possible, with a close look at various options for rendering text. If the screen display is of poor quality and lacks subpixel rendering, then opt for graceful degradation by serving system fonts to older browsers and OS. Conditional comments are the easiest way to exclude older browsers and operating systems from style sheets with Web fonts. Of course, JavaScript is a more elegant way to detect whether a client’s subpixel rendering is turned on."
Smudge, this is awesome feedback. You probably noticed in our comment above we've just launched this week, so this is much appreciated. If you see anything else, feel free to fire away. We'll be working to address these issues this weekend.