For those interested in other lightweight implementations, I have not yet had a chance to compare this but have been very happy with cJSON by @dave_gamble for extremely resource-constrained embedded microcontrollers.
Ditto. Found it easy to use and integrate. I needed something lightweight for a highly nested numerical model containing numbers and descriptive strings. I didn't want the Json bit to have a big footprint because the numerical computations make the software complex enough as it is.
I've used cJson for a couple of projects as well. No complaints here.