Diane makes an excellent point that no one appears upset with the D.C. Circuit's reliance on foreign practices in the recent currency case.
In my view, the lack of reaction helps to confirm a theory I offered in a blog post in 2005 in response to an essay on the topic of citing foreign law by our own Deb Pearlstein: The opposition to foreign law isn't really opposition to foreign law per se, but rather opposition to citing sources and making arguments that clearly take sides in the culture wars. Here's what I wrote on the topic back then:
The real issue isn't sovereignty, but the culture wars. The Supreme Court's citations to foreign law have appeared in highly controversial cases at the heart of a national sociopolitical divide between (for lack of better labels) social conservativism and modern liberalism. The kinds of foreign countries that a Supreme Court Justice might know best mostly don't share this sociopolitical divide: in those countries, and especially their court systems, the views of modern liberalism for the most part have won out. In this environment, stressing similarities with foreign court decisions can seem a lot like taking sides in the culture wars.
When a Supreme Court opinion echoes a side in the culture wars, the other side naturally gets very upset. Witness the very strong reaction from pro-choice commentators to Justice Kennedy's opinion in Gonzales v. Carhart in 2007, which at times spoke about abortion using language and arguments from the pro-life side of the debate. The angry reaction to Kennedy's language in Carhart was quite similar to the angry reaction from conservatives after Kennedy cited foreign law in cases like Lawrence and Roper .
By contrast, the culture wars weren't in play in the D.C. Circuit currency case. There isn't a progressive or socially conservative approach to currency size. Sometimes a dollar bill is just a dollar bill. I think that goes a long way toward explaining why no one seems to be upset with that part of the opinion (in addition to the fact that the opinion was statutory, not constitutional—presumably that helps).