Did they do any experimentation with pre-caching new content? What percentage of those new photos each day end up being requested I wonder.
I'm not sure if Wyatt, Qi, et al. looked at pre-caching at all. I've not looked at the numbers yet, but it's on my list of things to look into once the next few months of more obvious wins are worked through.
I'm not sure whether a "refresh" (ie, 304 not modified due to expiration) is counted as a miss in this data.