The post office is one of the more unique buildings. The action is changing ownership, and literally moving it from one corner of town to another. It's also the one action building that has an effect even if you don't use it.
Nat, I would be curious to know if the Post Office really did move around that much in historic New Bedford. As a postal worker and union officer at my local I do know that the USPS has been messing with facilities (closing, moving etc.) now, but was there some historical basis for coming up this particular game mechanic?