At 10:30 this morning, I'd already had 8x the visitors of the previous day. That's not so predictable. According to the referrers, most of the hits came from Twitter. With all of the link shortening that happens there, though, it can be pretty damned hard to find the source. With some clever searches and digging, I finally found it. @petapixel, with 54K followers, linked to it. There were several dozen retweets from various people. The whole thing turned into a nice little traffic spike-- so far today I've had over 13X the traffic of yesterday.
There was a nice spike on 5/16 as well. Someone on MetaFilter was looking for the site but couldn't remember the name. He gave a description, and someone quickly gave him the URL.