Do you have the HUD turned off?
That's where auras that are detrimental to you are displayed (i.e. debuffs on you and buffs on hostile targets). When targeting a hostile (i.e. a boss), the buffs on that target are shown at the top right of the health bars in the HUD.
EDIT: This post should help...
http://www.wowinterface.com/forums/s...ad.php?t=21108