Just look at the curve on that graph. Instagram users uploaded over 10 million Thanksgiving-related photos last Thursday. At its peak, over 226 photos (the majority of which were probably greasy food porn snapshots) were posted on the site per second.
Instagram, as you may recall, was bought by Facebook for $715 million earlier this year. Although it's still not clear just how Mark Zuckerberg plans to monetize the photo-sharing site, Forbes points to a change in its data use policy that will allow Facebook to use information gathered from Instagram's users - in this case, that a lot of them like eating roast turkey on the fourth Thursday in November--and use it for targeted ads and sponsored pages.