International cross-sectional data are a headache, as are data about comparative migration. Stalker's Guide to International Migration is, nevertheless, appealing.
The Guide cites the UN as the source for the fact that 175 million people now live in a country not of their birth. For the US, it is 11.1% of the population (2001) which is 32 million which is 18% of all the world's foreign born.
People can be expected to migrate to the richer places. In the years 1998-2001, the G-7 nations took in 10.6 million immigrants. Most (30%) went to the US. Germany with its relatively open borders took in 25%. As a proportion of its native population, Germany took in more. In fact, as a proportion of native-born population, the US was fifth of seven -- just ahead of Japan and France.
While the picture is complicated by policy differences and geography, looking at how people vote with their feet is always instructive. Open borders are interesting but so are open cultures and open markets.