In reply to the sheep:
I've got five in a row - works fine - you can spend what you want on hooks, but I've found the Decathlon ones to be both solid and cheap at about £4 each.
The trick is to get the off-set right (i.e. the bikes alternate between high and low). Bikes with mudguards should be high. Take account of up and over garage doors - the swept path of the door as it comes up intrudes quite a lot and makes locations near to the door unsuitable, and most are lower than you think when you hoik a bike up on end.
It's a bit of a balancing act getting the spacing between bikes right so that you can get one out without them getting too tangled. I have about a third of a bar overlap on mine.
No damage to wheels - 7-8 kg of bike hanging from a wheel that has your weight on it as a matter of course is nothing - bearing in mind that you hanging it from the strong points where the spokes apply their load. Hooks have rubber coatings too. Only wheel I'd be wary of are some of the esoteric wheels that have aero 'covers' on a standard-ish rim. Disc wheels obviously unsuitable without ill-advised modification.....
PS - the low bikes have their back wheel on the floor - high one dangle. Heavier bikes obviously better if they're on the floor from a handling perspective, but if they have a muguard, that's going to get in the way. It's a darn sight easier getting the locations right with an assistant.
Post edited at 12:10