I'm not sure if you guys are already working on this, but it would be nice to detach and move around the party window. When I am supporting as a mage, I often times buff myself and use it as a timer. For example, when supporting a tank in a boss fight I will immune him then immune me. When I start to see my run out I know to reapply immune to both of us. A lot of the time it is easier to just use the party window rather than try to heal/buff through mobs. This means I need to keep an eye on both my current buffs and the party health. I can fell my eyes starting to drift apart trying to keep track of both spots.
Seeing what Mephi just said about the mana bar... I don't think the detachable Party window is going to work.
So, maybe just the ability to move the buffs? This would also have the same effect of moving the party window and buffs closer together.