I've discovered that bottles fit in my storage fridge much more efficiency if I stack them horizontally, and I'm thinking of building some wooden racks to let me fit more bottles safely and securely.
I know it's considered best-practice to store bottles upright to allow yeast to settle and to reduce surface area inside at the bottle, but how much difference does it really make? This is for medium- to long-term storage: generally for less than a year, although a couple of bottles I've had for several years. Virtually all of my beers are capped, so cork lifetime isn't a concern of mine.