If I add the CPU monitor part of multiload_applet to my panel, I can configure it, and it works just fine. However, it will not reappear if I logout and log back in again. FWIW, this happens even on a completely fresh install and a brand-new user, so it doesn't appear to be related to any older GNOME files lurking about...
Could not replicate this problem with the gnome-core shipped with Red Hat 6.0.