Yes, there was a pretty good science show on that went over the options pretty well, concluding that just trying to blow the thing up or off path probably wouldn't work, and would tend to make the situation worse. The general consensus is to try and steer the projectile out of collision path using a propulsion system that wasn't too abrupt so as not to create acute stress levels that might cause structural failure and fragment the object. That of course assumes we detect in with sufficient time to deploy such a system and the thrust applied long enough to clear the object out of path.

Nukes might disintegrate the smaller objects capable of surviving the atmosphere, but then you would have nuclear fallout raining down with the debris stream. The planet killer sized asteroids cannot be destroyed by nuclear munitions currently developed and capable of being deployed in such a manner. Regardless, we don't have anything that could deliver a nuke payload effectively as an interceptor, though the technology is there to build one if we wanted to. My guess is it will be another hundred or so years before we could begin deploying an effective global defense system that would fairly eliminate the possibility of a strike.

What's interesting is that only in the last 40 years have we had sufficient technological development to be able to even contemplate such a task. It is a race; to see whether we can develop quick enough to prevent our own demise, while also avoiding being the cause of it. At no other point in time has there been a species capable of changing their own fate so. It is amazing that we might actually pull it off in the span of one lifetime.

Sometimes I think we may actually learn how to live forever. Imagine how far science has come in the last 200 years, and how far it will advance in the next 1,000. Most Science fiction really only deals with future in the near term, but what about a millenium from now, assuming nothing disastrous were to happen in that span. If our technology were allowed to continue developing contiguously for that long, what limits that we know of today can be overcome? In time, I believe anything and everything is possible.