Lots of things already mentioned. I'll just add one more.
Clojure if treats Java Boolean objects always as true even if it's value is false. So if you have a java land function that returns a java Boolean value, make sure you do not check it directly
(if java-bool "Yes" "No")
but rather
(if (boolean java-bool) "Yes" "No").
I got burned by this with clojure.contrib.sql library that returns database boolean fields as java Boolean objects.
