The Slime developers encourage users to run straight from CVS. Apart from being laughable, this is incompatible with the idea of running code in a production setting because it interferes with stable, repeatable deployments. For Swank Clojure we picked a revision of slime.el that worked well and coded against that. The trunk of Slime has moved on and introduced incompatibilities, but Swank Clojure has not because the effort involved in constantly keeping up with Slime trunk would not be in proportion to the benefit received. It does present difficulty in connecting to both Clojure and Common Lisp from the same Emacs instance, but in practice most Clojure users lose interest in CL and don't mind. It's possible to work with both if you use M-x clojure-jack-in for all your Clojure work and avoid loading your CL-specific configuration for trunk Slime until the time you intend to use it. You still can't keep them both in the same Emacs instance, but you can use the same Emacs config and just keep them in separate processes.