My N800 was running off-line for quite a while. During this time I’d listened to a bunch of songs with Kagu and was hoping that it would immediately scrobble them to last.fm as soon as I went online. After much fiddling around, I discovered that you must play another song in Kagu while online, in order to launch scrobblerd (via dbus). This, in turn, submits all the tracks queued for scrobbling while offline via maemoscrobbler.
I found some helpful maemoscrobbler tips in this #maemo IRC log.