For the first time since their introduction four months ago, Apple is offering refurbished models of the 27-inch current-generation iMac, at savings of up to 20 percent. Reflecting the constraints that have dogged the model since its introduction, the 27-inch refurbs list a 1-3 business day shipping window, and appear more than two months after Apple began offering refurbished versions of the 21-inch model. Following reports of a production breakthrough, iMacs of both sizes have appeared in greater quantity in the last month.