I have a feeling this is a bug on all MBA 13" models running ML & Safari 6. Go to Twitter Bootstrap site, and have a look at the buttons, and form elements. Are yours missing the right hand borders on some elements like this.... It might not happen on these exact element, but check the right hand border of all inputs, boxes and buttons. This is just an example, but its happening across all sites on the net. Interested to see how many have the same problem, and if you do please report it to Apple to help ensure it gets fixed!