The application is about 1300 lines of code, which includes all of the (Clojure-generated) markup and styling.It's built with Clojure, ClojureScript, and Datomic.
I'll touch on:
+ designing an application around Stuart Sierra's "Reloaded" workflow: http://thinkrelevance.com/blog/2013/06/04/clojure-workflow-reloaded
+ basics (and not-so-basics) of the Ring HTTP model
+ using Chas Emerick's Friend library to handle web user and API authentication
+ deploying/monitoring a Clojure application in (low-stakes) production
+ structuring an application around protocols so that service backends (e.g., S3) can be easily swapped between development, staging, and production
If there's anything that seems particularly interesting to you (in the above list or otherwise), please reply to this thread so I can prepare a bit of material.
I'm planning on giving a 20 minute high-level overview of the application, and then opening it up to questions and focussing on whatever topics folks are interested in.