I've been looking at PBs for 6 months, but haven't pulled the trigger yet. Kept waiting for an update, then the 12" didn't get one, so thought about getting the 15" until I heard about the screen issues. I'm a developer, graphics, web, flash, video, so the screen is HUGE issue to me if it's noticeable.
It's noticeable...especially if you ever work with images with images that have a "scanline" effect in it. It just doesn't look accurate. Also, even using iPhoto you can see the lines on every single thumbnail. It's frustrating when the older models didn't have these lines.