I think I have found a web rendering bug for Google Fonts in Mobile (iOS 8) Safari. It seems to me that Mobile Safari adds a tiny bit of letter-spacing to all text that uses Google Fonts, or that it uses another font. It doesn't matter which Google Font I try (Open Sans). It renders correctly on all modern browsers. Tested Android, FF, Chrome, Safari.
Try to load this page on a iOS device to see what I mean. See also see code and screenshot. See this link for live review: https://dl.dropboxusercontent.com/u/430406/Temp%20%5Bok%20to%20delete%5D/Checking%20Font/index.html
<!DOCTYPE html>
<html>
<head>
<title></title>
<link href='http://fonts.googleapis.com/css?family=Roboto' rel='stylesheet' type='text/css'>
</head>
<body>
<h2 style="font-family: 'Roboto'">Roboto: Looks like it gets a bit extra line-spacing in iOS Safari, though this is not possible to find in web inspector</h2>
<h2 style="font-family: 'Arial'">Arial: Works fine in iOS Safari</h2>
</body>
</html>