NeilM's system looks better to me than just hanging them on the ceiling, since it divides the weight of the bike on two points. I just wonder about the 'stability' of the bikes, don't they have a lot of space to move?
The way my bikes are hung, the wheels of each bike make contact with the wall and the hooks just hold the bikes vertical. The bikes don't move at all while stored.
Spacing: All the bikes in the pictures are retro mtb's, with flat bars around 550mm wide. The hooks are spaced at about 10 to 12" centres. I did read that 8" was sufficient, but this put the bikes much too close together although it may be OK for a rack with only road bikes.
An additional note; all the bikes are locked together with a wire rope.
"Try not to punch any clowns"