This image is a screenshot from Font Awesome examples.
On my screen (and I even turned to Paint to make sure it's really blurry, not just some kind of magic) 90 and 270 degree turns seem blurry. Vertical and horizontal somersaults are accurate. My question is why ? What happens to Chrome or the Font Awesome mechanism that causes this?
Naturally, IE 9 is worse
The awesome CSS font defines the CSS rule that causes this problem.
.fa { line-height: 1; }
After removing this rule, the icon displays very well.