Ah. This isn't SLIME. As akkartik said, it's likely that no one here uses it. If you want to try SLIME, follow my instructions here: http://arclanguage.org/item?id=14998
I definitely use arc.el on a regular basis, though I won't claim to be familiar with the finer points of its capabilities. As far as I'm concerned, it offers reasonable highlighting and indentation for arc code; I haven't tried to get it to do much else. For most of my lisp editing needs, I rely on paredit.