The most noticable differences (apart from the rendering) are the fi ligature in the title ("overfilled") and the Q feature (where the tail is extended past the first letter ("Quisque").
Kerning is also better on OS X (with Firefox, Chrome and Safari 6), but it's hard to notice on the demo pages because, for some reason, the text body in the Google Fonts page is three pixels lower than in the Brick version.
I glanced at the CSS but couldn't find the reason.
