One thing that may be worth mentioning is the rails default use of jbuilder. I know jbuilder isn't JSON serialization bit, but if we're talking about things tha

One thing that may be worth mentioning is the rails default use of jbuilder. I know jbuilder isn't JSON serialization bit, but if we're talking about things that make rendering JSON in ruby/rails slow, jbuilder would be top of my list. If you are rendering many partials with jbuilder, things really slow down.