Binary plists over the wire? That's a hardcore innovation that I will file away in the back of my head for next time I'm building a backend for a mobile app.
All credit to Apple's WWDC 2010 session on building server driven applications. Great stuff in there, grab the video off of iTunes U if you've joined the developer program. Among other things, they break down the performance of various payload formats.
Most JSON frameworks are faster than binary plists on iOS. I learned it the hard way, after spending a day writing a Python module for the server side and doing some tests. However, binary plists were around 5% smaller, so they might help if your bottleneck is the bandwidth (it wasn't my case).
