Hotkey "popup last unread message"
Gajim's mode "only show incoming messages in roster" is very useful from the point of view "I'd like to read all IM messages when I want to, not when my buddies want it". However, it's hard to find "what's new" when your roster is big.
I would propose some keyboard shortcut which pops up single unread message, behaving exactly as I do by scrolling roster, searching for the contacts with unread messages and clicking on them.