After today's patch (0.3.23), the PD (and PD behavior) is still very inconsistent.
On stations, it's incredible, using its full range and attack speed to shoot down volley after volley from entire fleets.
On ships, however, you can have 2 ships alongside each other in a tight formation, and if the enemy shoots one, the other ship's laser PD will not fire at all, letting his ally die to 3 missiles that randomly flew its way. Batteries are full, radiators are out, but it just doesn't shoot.
Same thing actually happens if you use bigger laser batteries for PD purposes: they're all set to the Guardian mode (green icon), where they should prioritize enemy projectiles over shooting enemies, and the ships are in overlapping defense cloud, but they just don't shoot the incoming barrage, instead waiting until the enemy gets into maximum range and shooting at the ship.
Just had this in a fight where I had Arc Laser PDs and a bunch of UV Laser Batteries (the 2 slot ones).
This makes it so making a defensive cloud is impossible because the ships simply do not shoot the incoming projectiles down.