Helm for Emacs is a fantastic Quicksilver-like extension, but it gets quite wordy sometimes. Instead of C-u M-x helm-do-grep *nav to dir* *enter extensions* *enter query* to recursively grep, I defined the following in my init.el. Now hitting F1 will grep actual source across all my projects.

(defun project-search ()
  (interactive)
  (helm-do-grep-1 '("/home/vaughn/src")
                  '(4)
                  nil
                  '("*.clj" "*.cljs")))

(global-set-key (kbd "") 'project-search)