Well, in terms of missile defense, I don't really think you can say he is "destroying" missiles. He is basically looking to shift away from the GMD system and move towards a more robust Aegis crisis capability and a deployment of SM3-BlockIIA. That missile is currently in development, and he has cut some funding for that, which to me shows that its deployment (and by extension a credible missile defense shield) is not a priority for the White House.
He also eliminated the ABL and thte MKV. The ABL I did not have a problem with ending that, but I think the MKV is imperative to any missile shield, so I was disappointed to see that.
So, in terms of missile defense, he did stop the deployment of some some missiles as part of the GMD framework, but (in theory at least) he will deploy the SM3-BlockIIA by (if I remember right) 2015. Ultimately, I think his missile defense plan was better than the Bush plan, but my problem comes that he is not really making it a priority, and I think deployment will be delayed far beyond his proposed time frame.
There was the treaty signed with Russia to destroy a number of I guess old missiles and I did not think there were any new ones being made by us. PLC1 seemed to disagree with me. He did post a link that I never read I got too busy.
I assume you are talking about the new START treaty. You are correct Obama has signed the Treaty, however the Senate still has to ratify it to have any effect... that will require 2/3rds of the Senate, which will require some Republican support.
Now, the biggest complaint I have seen against the treaty is the conversion of ICBM solos to missile defense sites... but I don't think that is actually going to be a problem in the military.
My problem with the treaty is that is basically allows the Russians to maintain strategic nuclear parity with the United States, and at the same time, language was included (while non-binding I believe) that will limit American missile defense capability. So ultimately we are left with strategic parity with the Russians, but it ignores the problem of shifting Russian views to more of a tactical nuclear arsenal, which will not be covered. If that is ignored, then any new arms agreements is really meaningless in my opinion.
Basically, in terms of nuclear parity, it puts the US behind Russia, and while that does not mean a ton, it can be important in terms of a credible nuclear umbrella, which helps to prevent further proliferation globally.