After the recent changes to slime-output-buffer (2005-09-15), the REPL history is no longer preserved across inferior lisp restarts. I don't understand the code well enough to know what the proper fix is, but the following kludge seems to restore the old behaviour:
--- slime.el 27 Sep 2005 22:42:55 -0000 1.552 +++ slime.el 1 Oct 2005 19:41:09 -0000 @@ -2474,7 +2474,8 @@ (setf (slime-connection-output-buffer) (let ((connection (slime-connection))) (with-current-buffer (slime-repl-buffer t connection) - (slime-repl-mode) + (unless (eq major-mode 'slime-repl-mode) + (slime-repl-mode)) (setq slime-buffer-connection connection) (slime-reset-repl-markers) (unless noprompt