Before beginning a McCLIM session with CMUCL, you are strongly advised to initialize multiprocessing by evaluating the form:
(mp::startup-idle-and-top-level-loops)
If you use the SLIME development environment under Emacs, evaluate the above form from the *inferior-lisp* buffer, not from *slime-repl[n]*. Initializing multiprocessing can make a difference between an application that starts instantaneously on, say, a Pentium IV class PC, and one that may take minutes on the same machine.