Other then the obvious (not being easily able to see / change the code of the OS, FS, GUI, networking stack and the editor using its own, pre-CL Lisp dialect), what's missing from a Linux/MacOS + Emacs + Slime + SBCL/CmuCL/CCL environment? Does it really make a difference to an application developer? How do the offerings of Allegro or LispWorks compare?