Day after US Thanksgiving here (Black Friday), sipping a beverage and idling through the playbox2d source code - happily discovered that collision detection is in fact supported:
world:getNumberOfContacts(body1, body2)
...tested that in a minigame testbed and it works a treat.
While looking through the sources I was also wondering 'what's this Arbiter thing all about?' - and found a slide deck ('Arbiters' towards the end) that I share here in the hopes it might prove useful to folks using playbox2d: Fast and Simple Physics using Sequential Impulses
Happy holidays!
Edit: Really enjoying this... mini-game update using Playbox2d
here.