I have one friend I've always sent postcards to - not every trip, mostly just from vacations. She lives in the US midwest and is unlikely to ever do much travelling (funding, or the lack thereof), and says she loves getting to see different places in the world and know that someone she knows has been there.

But I really like the idea of sending them to kids -- I don't have any (kids, that is), but I bet some of my friends' kids would enjoy, thanks for the tip!