TDD is about fast feedback. CIDER tightens the feedback loop with quick commands for running tests and a powerful test reporting system.
Lambda abstractions are always leaky, but some are leakier than others. Clojure programmers recommend keeping most of your functions pure and containing the leaks as much as possible.
Function application is a key concept in lambda calculus. While it is commonly expressed using parentheses in Clojure, it is also reified into a function which itself can be applied to another function.
The world may be mutable, but people have been using the notion of immutability to build reliable systems for a long time.
I made a clojure.test cheatsheet that you can get for free.
Ront Toland will talk about developing large Clojure applications.
Nathaniel Smith and Ruth Linehan will talk about developing large applications in Clojure.
Leon Barrett will talk about parallel programming in Clojure.
Priyatam Mudivarti is giving a talk about grid systems in Garden.
Elango Cheran will talk about translating Clojure to other human languages.