It's 3 am, and you have a hankering to mail a letter. But you really should be in bed, so you want to mail the letter in the closest possible location. You know there's a box a few blocks away, and there is the post office a few blocks in another direction. Is anything closer? You rack your mind, trying to imagine those big blue boxes.
The USPS website has nothing. It just tells you where the nearest post offices are. But it won't tell you about the drop boxes.
Finally, google springs into action and delivers a mailbox locator.
Even cooler is the mashup map of all the mailboxes in your zip code.
The nearest mailbox is really just a block and a half away. You can't believe you don't remember it, since you run by there all the time. In any case, you drop off the letter, come home, and sleep content in the knowledge that your mail will go out tomorrow.