Improve contact popup
Google Talk has a very nice looking contact popup which shows an enlarged contact avatar and a minimal set of detail. It also pops up to the side of the roster window (kind of like a popout) instead of at the mouse pointer position which is kind of nice. I will post a screenshot if I am able to add an attachment.
I think that the contact popup in Gajim could be improved. Currently it shows a lot of rather technical looking information (which honestly is helpful) and some redundant information which could be reorganized or removed.