Between riff 60 and 61 he tunes to drop-D in a single twist of the peg, and then later goes back to a standard-E, without ever losing tempo (he does it again at 72/73 and 75/76). Unbelievable. Also, the way he deftly picks up the slide for Seven Nation Army #88 while holding a hammered note with his right hand is fairly impressive.
I was surprised and pleased by his pick for #100.
Some friends and I were discussing recently how different technical proficiency is from "soul" or whatever characterizes the musicianship of great artists. (See: Steve Gadd vs. just about any other dude trying to teach a Steve Gadd rhythm.) Alex seems to have a feel for all of these songs beyond technical rudiments. I get the sense that he could play any song with a band and have groupies waiting backstage. Is this because Alex is a musician and the aforelinked drummers are merely technicians? Is it easier to fake "soul" on the guitar than the drums? Something else?