New Apple product stock keeping units (SKU) have leaked that indicate that at least one of Apple's MacBook lines is about to receive an update. Though nothing is definitive, 9to5Mac believes that these SKUs point to a refresh for both the MacBook Air or the MacBook Pro with Retina display.
These SKUs likely belong to an Apple notebook that comes in two screen sizes. Each screen size will come in two configurations that will be diversified by internal specifications like processor speeds, RAM, and storage space. Currently, Apple sells two notebook lines that fit a refresh with these SKUs: both the MacBook Air and MacBook Pro with Retina display.
Both lines come in two different screen sizes, and supplies of both the Air and the Pro are constrained. The codes are only for one computer line, so it is unknown if both will receive a refresh or not. Supplies of the non-Retina MacBook Pro are not constrained, meaning that a refresh is most likely a long way off, if it comes at all.
Apple refreshed its entire notebook line and revealed the MacBook Pro with Retina display during their keynote at the beginning of WWDC 2012. It is likely that if a refresh takes place during the conference this year, that it will happen during the keynote as well.