At monkey music with ds and saw a lady put her two kids in a pushchair, couldn't see the second child - it was a phil and ted (I spose you'd call it a tandem but it wasn't really!) and the other seat was UNDER THE PUSHCHAIR!!!!
I'm probably the last person on the planet to see one but I'm truly shocked! Granted, it made it a nice small (smaller than most tandems anyways) pushchair but the poor second child would see nothing!