Shoutbox

This feature would have to be part of Messenger itself for it's sheer complexity (and the fact that you would want to reproduce what the contact list looks like when you use a different computer).  Unfortunately though I doubt this feature would be added to quickly as the likes of subgroups have been asked for for a long time now and it seems like a far easier feature to implement so I can't see what you are asking for will be implemented too early.  I think this would be a great feature to have but it's just hard to get someone to do it.

Also another way of looking up people in the contact list can be by using the edit details part of each contact and adding in some notes or other details and using the 'contact scroller' I think it is called (the search part next to the add contact button in the contact list).