'Hybrid' mode - group online contacts normally, with offline group for all offline contacts.
This is something that aMSN has and I found useful when I used aMSN. It basically means you can see all your contacts if you want to go check a history or something, but you don't clutter up your online groups with people who don't talk. I know there's some issue with how Gajim handles groups, and that it musn't tell the server that all these contacts are in an Offline group :P