So, of my two revB MBA's, only one has lines. After bringing them both into the genius bar and setting them side by side, the genius agreed that there were faint lines visible on light backgrounds, and is having it sent off to have the whole top housing replaced. Here's to hoping that it works out... UPDATE: so despite the fact that I have some authorization from the genius bar to have my clamshell assembly replaced, I just checked the status of my order and it says "no issues detected." I'm assuming that apple is within their right to do this, but the paperwork clearly states that the lines are visible in store to multiple geniuses. I'm thinking about taking my paperwork to my local Apple Authorized Service Center and having them do it. They're usually glad to have the work, and I'm assuming that they'd just bill Applecare? Thoughts?