4 and only because I lived or worked there.

I know all the postcode districts of East London because they were designed to be in alphabetical order.

Four. Two because I lived/live there, one because I went to school there, and one because it is where I work.

Not sure - probably about 20 or so I guess, maybe even more. Mostly because, about 10 years ago, my job included sending out promotional material to people responding to newspaper ads (remember them?) throughout my city and surrounding areas.

Only the places I lived, really. When I worked in administration at summer camp I had a pretty good mental catalogue of Phildelphia zip codes and the neighborhoods they represented - only because most of our campers came from Philly - but my brain promptly discarded that after I stopped working there.

I also remember ZIP codes for Children's Television Workshop (Sesame Street) and ZOOM because they were oten repeated on TV when I was a kid.

Only two. My own and where my mom used to live. Any others, even for close friends/relatives, I always have to look-up, because the zip areas are so crazily drawn. They don't adhere to distinct "neighborhoods" in any real or practical sense. At least, not in my neck of the woods. Zip code areas here resemble gerrymandered voting districts more than anything else.