I'm just a bit confused about what the most stable release of LuaTeX is at the moment and where to get it ... from Pragma or the garden?
Neither. The source for the LuaTeX binaries is the Supélec GForge repository (cross-referenced from luatex.org): http://foundry.supelec.fr/frs/?group_id=10 It contains binaries for every beta version, not only the latest one; but as a rule you should better take the latest beta release if you have a recent ConTeXt: Mark IV often relies on very recent LuaTeX features, so older binaries will *not* run smoothly, on the contrary. The current version is beta-0.20.2. I build the binaries for Mac OS X myself each time Taco releases a beta (I compile on Tiger, but I expect the binaries should work flawlessly on Leopard -- if you experience problems, please report). Arthur