For our production blog, we keep wordpress and all plugins in svn. This means we keep the cache directory as a symlink to somewhere out of the actual source tree. We got this working with WP Super Cache 0.9, but upon attempting to upgrade to 0.9.4.1 today, it's presenting me with a new error:
Warning: mkdir() [function.mkdir]: No such file or directory in /Volumes/WebServer/blog/src/wp-content/plugins/wp-super-cache/wp-cache.php on line 901
Error: Your cache directory (/Volumes/WebServer/blog/src/wp-content/cache/) did not exist and couldn't be created by the web server. Check permissions.Cannot continue... fix previous problems and retry.
This isn't exactly true -- cache DOES exist and points to a chmod 777 directory. I note that line 901 is in wp_super_cache_disable() in wp-cache.php.