Addition to nRepl.el for showing number of live threads in mode line.

gistfile1.el

;; Eval all this in the scratch buffer, then have a play with evaluating forms in a clojure buffer.
;; This is a very quick and dirty first version.

(setq thread-count 0)

(defun add-remote-thread ()
  (setq thread-count (+ 1 thread-count))
  (setq mode-name (format "Clojure{%d}" thread-count))
  (force-mode-line-update))

(defun remove-remote-thread (buffer)
  (with-current-buffer buffer
    (setq thread-count (- thread-count 1))
    (setq mode-name (format "Clojure{%d}" thread-count))
    (force-mode-line-update)))

(defun nrepl-eval-expression-at-point (&optional prefix)
  "Evaluate the current toplevel form."
  (interactive "P")
  (let ((form (nrepl-expression-at-point)))
    (add-remote-thread)
    (if prefix
        (nrepl-interactive-eval-print form)
        (nrepl-interactive-eval form))))

(defun nrepl-interactive-eval-handler (buffer)
  (nrepl-make-response-handler buffer
                               (lambda (buffer value)
                                 (message (format "%s" value))
                                 (remove-remote-thread buffer))
                               (lambda (buffer value)
                                 (nrepl-emit-interactive-output value))
                               (lambda (buffer err)
                                 (message (format "%s" err)))
                               '()))