It was used as the primary armor on the Leopard II tank. The holes are drilled at a sloped angle relative to the expected direction of impacts from the top, and are smaller then the diameter of expected threat sabot projectiles. So when a sabot reaches the holed area, it is subject to asymmetric forces and always meets some resistance, encouraging its own erosion. The end result is that protection per weight improves considerably. How much would depend on the exact details of the incoming projectile, as it always will when considering special armors like this. I've heard 70% resistance for 50% of the weight claimed as an average, I have no idea as to the validity of this claim.
Against HEAT the armor protection is generally reduced, though it depends on the exact hit placement. The point though was the Germans thought AP shot from tanks was a bigger threat then HEAT missiles while fighting on the defensive. Missiles could after all be countered to a considerable degree with counter fire and smoke screens due to the considerable times of flight, while you couldn't do much about a well aimed Soviet AP shot. You also could repair perforated armor easily which was a big plus when fighting outnumbered. The British and Americans disagreed about the threats and so used Cobham which was much more effective against HEAT. Ultimately Cobham was improved in various manners to increase protection from sabots, while the Germans improved perforated armor vs HEAT by filling the holes back in with lightweight composite or similar materials. Other changes were also made in the long run, such as the Leopard II now has that big wedge of spaced armor on the front of the turret.
[/size]This sort of armor could be produced in WW2, or WW1 for that matter, but it is not very realistic for war use. First, it’s only going to work well with fairly thick slabs of armor, thinner plates will loose too much stiffness and yet even most German tank armor simply wasn't all that thick in WW2. It also just requires a vast amount of drilling, and drilling steel armor requires large machine tools and lots of tungsten drill bits. It also simply requires a great deal of time in the manufacturing plant. All three were in short supply during WW2, and drill bits were not as good as they would be in the 1970s.