Just kidding :)
Congratulations to Chetty! He's done lots of good work, but one area I've found particularly interesting is the divergence of macro and micro labor supply elasticities. I first got into this when I was looking at the Georgia tax credit with aggregate (county level) data and thinking about whether I should be thinking in terms of macro or micro elasticities. The literature around the measurement and reconciliation of the two is fascinating stuff.