Thanks to Mike Leahy for spotting this:
http://blog.gemserk.com/2012/02/02/how-we-use-box2d-with-artemis/
…a short blog post (with code) on how a team is integrating Box2D (a very well known open source physics lib) with Artemis (a java implementation of Entity Systems which starts from the same point as my Entity Systems posts, but fleshes it out)