In the few games that my group is playing in. We're finding that any armor pretty much amounts to squat in the current rules, especially vehicle armor. The problem we have is with the net hits adding to DV before the damage calculation.
For example: It seems odd that a Predator IV can cause damage to a patrol-1 (armor 10) with 5 net hits, but not with 4. The net hits adding to DV before comparing to armor also basically eliminates the need for the called shot options because by the time you'd need to use the bypass armor option or the +4DV option, you'd be subtracting too many dice for the former and the latter wouldn't make enough difference.
Considering the general level of dice pools in SR4, its not impossible or even uncommon to be able to roll 12-20 dice with standard 400 bp characters. This means that a light pistol with standard rounds could take out a steel lynx or a car in just a few shots.
So, with the problem laid out. We've come up with the following house rule: (We're still trying to decide if it should apply universally on only to vehicles, but I think it should work well either way)