I think that instead of doing,
(defn non-blank? [line] (if (re-find #"\S" line) true false))
a more appropriate solution would be.
(defn non-blank? [line] (boolean (re-find #"\S" line)))
It introduces a new function but prevents newcomers from thinking that (if foo true false) is acceptable style (I personally get cold shivers when reading code like this ;) )