That was my first question, what are the occasional big spikes (not the weekend drops in traffic)? Interestingly, spikes in page views and unique page views do not correspond well, although sometimes they're slightly offset from each other.

As minimaxir says, this is the weekends. Amazon.com gets big traffic spikes during the typical work week, I suspect HN's traffic spikes are the same effect =).

I believe the big spike a year last Nov/Dec was the cricket bat story that went mainstream media. The one after, was that _why going offline?

Steve Job's death on Oct 5 is about as big a real spike as I'd expect to see.

Presumably some of those correspond with the start of funding cycles.