Three systems, one in each of the places in my house where I spend a good deal of time, living room, office and garage workshop. All of them are tied together by WiFi so that I can move from place to place without any interruption in what's playing.
What made you put together your first 2nd system?
Did you just have lots of spare equipment and figured why not? Did you have a spare room, hobby room, shop, or office that needed better sound? Did you want to set up separate music and home theater systems? Or digital and vinyl rigs?
What was the final thing that pushed you over the edge?