In the hands of oppressive governments and out of the hands of those who might oppose them. Fox News has an article about the possibility of Obama using the Arms Trade Treaty to fight for gun control here in the US.
I don't doubt that many wish the US would ratify the treaty, but given the makeup of the current Senate the best (from their viewpoint) that is likely to happen is that the US will become a signatory. Even though the US often follows treaties to which it is a signatory (a point brought up in the article) it is only obligated for follow treaties if 2/3 of the Senate choose to ratify it.
The treaty is a joke, a sham. If it does anything at all, it will be to strengthen despotic regimes and weaken any resistance to such. We must remember that this is the same UN which has in the past placed China and Cuba on their Human Rights Council, and which currently contains several members which Freedom House rates as "not free", such as Angola, Qatar, and Congo (not sure which one, but it doesn't really matter).
Given who they place on their Human Rights Council, no one should expect anything good to come of any treaty that comes from the UN.
Read the entire article - it has good points from multiple individuals about the whole issue.