Spent a good amount of time messing around with CMUCL trying to make a bot for a MOO we use at work called Lily. I'm not quite sure how to do I/O multiplexing on a network socket and standard input, but I think I'm making progress. It's fun to actually make a useful program in common Lisp instead of just reading about it. I tried to use dan's DB-SOCKETS package, but I couldn't get it to compile in my CMUCL.
My interest was renewed after reading Erann Gat's old PARCIL code, which implements a simple C evaluator. It didn't look too awful painful, so I figured parsing the Lily protocol wouldn't be impossible.
Also recently learned that Paul Graham's Viaweb setup gave every customer their own Lisp image! That's one way to avoid problems with multiprocessing.