Personally, I don't think UN resolutions are particularly relevant unless they're backed up by something, and they usually aren't. For the most part, it's just a bunch of international bureaucrats with delusions of grandeur, who aren't any more effective than their predecessors with the League of Nations who had similar delusions of grandeur.
Nevertheless, I'm trying to figure out what's so bad about abstaining on this vote. Most people on the Right are just ripping it because we didn't vote with Israel and because they don't like the UN in general (and for good reason). Well, unless it's per se wrong to ever vote against Israel, then that's not much of an explanation. (I think some conservatives actually do think this, because they think there's a religious duty to support a Jewish state. I think they're wrong both on political and religious grounds, but that's another discussion.)
So I wonder what part of the Administration's explanation is wrong. Has hostility toward Israeli settlements not really been part of US policy for the last several decades? (In other words, did Ambassador Power lie?) Did the resolution do more than just condemn the settlements? And I'm serious. I honestly don't know the answers to these questions.