Green's slides were the most surprising. I was just about to nod off after an initial inundation of stringy mumbo jumbo, when I saw the words
natural $SL(2,Z)$ generalization of Riemann zeta values.Recall that so called zeta values are usually values of the Riemann zeta function for integer arguments. In M theory, these integers are 1-ordinals in the sense of Batanin, and are associated with 1-categorical structures. Now awake, I noticed the reference to the paper by Green et al on MZVs, which I may get around to reading eventually. The appendix is written by D. Zagier!
Update: Webcast here.