I was a big proponent of vertical stacking. Pictures and a description of my rack are in
this thread and a couple of other ones Mike listed so I won't repeat everything, just provide an update and a few additional comments:
Almost four years and many hundreds of board feet later, I am still convinced vertical is the way to go for all the reasons I stated originally.
Vertical may not be possible in shops with low ceilings. The ceiling height slopes from 8' to 10' in the area of my rack.
I added safety chains (almost too late :confused_ ) to the ends of the pipe.
I never added intermediate height bars.
Examine what kind of wood you will be storing and using, and how much of it. Most racks are not intended for wet wood or short pieces.
When I say I stack vertically, I don't mean leaning the boards against the wall. I mean stack them soldier-style with edges towards the wall.
I still need to build a (rolling?) bin for cutoffs.
(Photo taken before the addition of safety chains)