I was having some problems getting objects to properly serialize when using cl-prevalence, until I found that there was no implementation of serializable-slots for sbcl. This patch contains such an implementation. Also, I've modified it somewhat from the formula followed by the other lisps. Rather than simply returning all slots for the object, I only return those slots which are currently bound for the object. I leave it up to you to decide whether this is a useful addition or not.
Anthony W. Juckel