Your comment made me curious. I downloaded the complete last month (February). 28 days, every day has a gzipped json file which is on average 86MB. Summarized it is 53GB of gzipped jsons for 28 days. Roughly 700GB gzipped per year. Didn't have the chance to ungzip them all.
Wow I am shocked that they allow "firehose" access not only for free, but without even an API key.
Given enough disk and bandwidth, does this mean you could keep your own copy of all of github? I'd love to be able to grep the whole thing.