This works really well in Ireland. Eircodes (our late adoption postal codes) resolve to individual addresses rather than areas, so Irish sites mostly do this.
You have to be careful with this. Building sites (translate that into American as "houses under construction") may want to order stuff, but won't yet have eircodes. Indeed, I believe that they're issued only twice a year, so new-built houses may not have them either. So you cannot make it a required field.