I have a casio privia px330 digital piano with weighted keys which I use when out and about but have my acoustic at home. This may seem like a strange little question, but does anyone know if it matters which way up its stored? Horizontally (taking lots of room) or upright on end (taking less room?) I'm hoping it makes no difference either way!

If you store it up right then maybe the keys will suffer stress that they were not designed for (gravity from the wrong direction?) You could make the keys stick like this? I would like to know for sure too!

When I need to put mine away it goes back in the box it came in and slides under the bed.

I suggest you try asking on the pianoworld.com digital forum

My Yamaha digital piano says in the instructions it must not be stored standing up on its side or it could damage the instrument, so I would try and keep it flat.