What is important to add to dogboy's informative write-up is that mail delivery in Costa Rica is completely unlike that of the United States or many other countries. Very little mail is delivered directly to houses and the majority of people have post office boxes. Because of the bizarre system of addresses, it is not uncommon for mail addressed directly to homes to get lost, especially if landmarks are used that are unfamiliar to the post office. Or if there happen to be two or three white houses four blocks west of the fish market the post office will guess which one you are sending your letter to. This is why the vast majority of mail goes to post office boxes and not to homes. There is also no such thing as junk mail and the electric company, water company and telephone company generally handle their billing without the assistance of the post office. It is also rare to send checks by mail and bills tend to be paid in person. Mail is simply not as relevant in Costa Rica as it is in the United States and elsewhere.
A fun example of the address system is in San Pedro de Montes de Oca. On the main street of San Pedro, there used to be a very famous higueron tree, but one day the higueron fell down and was removed. Years later it is still used as a reference. If you weren't around before the higueron tree came down, then the directions you receive to addresses in that area will make no sense (the tree is used almost universally in directions to that area). Sometimes directions to a home or business will involve the use of two or three landmarks that no longer exist. However, pay close attention to the wording of directions. If the word "old" (or "antigua") is used that means it is no longer there. If you are in Costa Rica asking for directions and you hear someone refer to "the old embassy" or "the old hotel" request further clarification. Perhaps even "So, what is there now?"
Part of TheDeadGuy's series of nodes written mostly by Mrs. DeadGuy.