Part of the Postcrossing system is that you never send to the same address twice, and you never receive from the person you send to. However, at least the latter sometimes happens anyway, as I can vouch for. :-) In early January I got a card from Tanja in Turku, Finland, and then, only ten days later, I pulled her address as the destination for my 46th card. How is that possible? Because Tanja has three PX accounts, but the system thinks she is three different users. :-) So on January 15th, I sent her this card, showing some views of the Vigeland Park, one of the main tourist attractions here in Oslo.
Tanja is interested in seeing things that are special to the sender's city or country, so I thought she would like this card.
It had 640 kilometers to travel, and it covered the distance in four days to arrive on January 19th. Tanja's added it to her favorites, so my assumption was correct. ;-)