rubygems/rubygems.org — comment on commit 7699608ae2993a638f79b4aa00fe61ac8f6e511c
File:  line 0
By sferik:

We are using Yajl. We're just using it through the MultiJson interface. That way, if we ever want to switch what JSON library we use again (as we just did), we'll only need to make the change in one place (the Gemfile) instead of littered throughout the code.

Since `fog` already depends on `multi_json`, this seemed like the obvious thing to do. Basically, this is the reason why `multi_json` exists in the first place.