There are some pretty nice Lisp IDEs out there. All other things being equal (although rarely are they, of course) I'd probably rather work in Lispworks than, say, Emacs+SLIME+CMUCL for example. A lot of people like the Allegro CL IDE as well. While certainly not necessary, there's still a lot to be said for having well integrated inspectors, browsers, debuggers, and so forth, even for Lisp. And I'd think it'd actually be easier (quite a bit easier, actually) to make a decent Lisp IDE than one for something like C++.