I'm sure the SDI does mostly work. That if put into operation, it would hit most missles it was trying to intercept. However, whether it could get them all, questionable. And if just a handful get through in a nuclear attack from a fomidable power such as Russia, then the ones getting through could enough damage to still wipe out the United States. So, it can't just be 99.99% effective, it has to be 100%.

But I think that the SDI would be quite useful in battle, given the military prowess of the United States. Seeing that with a mere drone, they've been able to kill members of al qaida in the remote Arabian desert, then with SDI, it would probably be spectacular in its capabilities. However, war's not something I like to revel in, just speculate on what it can do. That's all.

...Now if the Americans could only build as decent a car like their WMD....

The alternative to the missile shield is nuclear bunker busting bombs to take out the nukes before they can be used. If N Korea destabilizes for whatever reason and Kim Jongil decides to push the button, well it would be great to break his button before it gets that far. If America decides to put pressure on Pakistan they may respond with developing wmds to launch their missiles. Bunker busting bombs would be great in that case too. The problem with bunker busting bombs is the fallout. With a missile shield there is very little to no fallout. The best solution of course is to stop nuclear proliferation.