I've recently begun saving postmarks from letters and giving them their own page in my stamp album. There's a certain thrill for us postal geeks when we find a perfectly preserved postal marking. This is especially useful when you come across old letters and you're trying to determine if the date reads '1918' or '1928'.
National Postal Museum store. I had not really considered myself a stamp collector, but now that I have an album with a few stamps in it, I guess I have to rethink that.