Plugwater is right in the point he is making. SAMs need to be battle proven. The US brought Patriots into their theater. All it did was fail to shoot down enemy missiles and shells and did very well in shooting down friendly aircraft like Tornados and Hornets. In other words it failed even after it was deemed operationally employable.
The only thing concrete against a ballistic missile is another ballistic missile. BMD is passive deterrence and we know "Deterrence is not warfighting."
The Americans have radars that can track cruise missiles from 3000Km away, even they don't promise fool proof security to their denizens. By end 2012 they will have global capability in tracking any aircraft, missile or rocket from only heat signatures using satellites. The Americans still don't claim fool proof capability against missiles and won't be claiming the same for quite some time. The Indian BMD, if it works even to 50% of it's claimed performance is a major success. Tracking and killing a BM is extremely difficult and there is no guarantee it works even after successful tracking.
Cruise missiles, once detected, are easy to kill. Fighters can chase and kill CMs using WVR missiles. A lucky gun shot will do the trick too.
Real BMD system that India will deploy is only after 2017 when Phase II is ready. Until then the Russian claims of BMD protection is more assuring and the Americans know the Russian BMD cannot stop their ballistic missiles.
The real purpose of a BMD is to force the enemy in an endless arms race in missiles. A 50% saturation probability will mean the Pakistanis will need twice the number of missiles as ADs or PDVs and we know ADs and PDVs are cheaper and faster to produce than Shaheen or Gauri. So, the advantage lies with us. Missiles also work at a 50% efficiency rate, so Pakistanis will need 4 times the number instead of 2.
^^ ballistic missiles by default aren't highly maneuverable.
Mid course maneuvering is a threat to BMDs. The maneuvering warheads on Bulava are probably the biggest threat of all. Combine it with electronic warfare and we have a recipe for disaster.
Edit:Aerostats are sitting ducks. They are great for peace time operations because of costs and are meant for that only. Aerostats tell the enemy, "We are watching you." Once a war starts, we need to pack them up or they will be the first to go.
Aerostats are completely useless for BM defence simply because they look down, not up like ground radars do. Aerostats are great for CM defence, but this is not very complex. Any radar which looks down can engage CMs.
Plug what happen to you. 
