With WoW's development as an e-sport, the need has arisen for a decent spectator UI for viewers and commentators. The goal of a spectator UI is to give the viewer a clear idea which team has the advantage at a given moment and to enable him to recognize the turning points in a match as they happen, rather than after the kill is scored. It's also important that the spectator not be presented with too much information. Blizzard's current spectator UI involves a default-style party frame on each side of the screen, one for each team. Obviously, there's a lot of room for improvement.
Here's my sketch of a better spectator UI, with a team status display for upper left/right and a sample unit frame:
The major feature of the team display aside from the obvious name/players/mana is the cooldown tracker. The cooldown tracker monitors the status of major cooldowns for each class: AP/PoM/Ice Block/Cold Snap for Mages, NS/EM/Mana Tide/Bloodlust for Shamans, etc. This information gives the spectator some data on the momentum of the match, letting him see that Team A has already exhausted most of its defensive cooldowns while A hasn't used its major offensive burst yet, or vice versa.
The unit frame is deliberately kept very simple. A large class icon, a health % display with arrows indicating the incoming DPS (more arrows = more DPS = higher pressure; probably just track damage taken over the last 5 seconds and recalculate). Mana displayed graphically behind health. One single large status icon indicating an immunity effect (DS, BOP, Ice Block), a CC (Fear/Sheep/etc), Spell Lockout (Holy icon with a red X?), or Drinking. Keeping the unit frame to a bare minimum, we want the viewer to be able to see who is under attack, how severe the attack is, and recognize when players are locked down leading to a kill or other clutch play.
This is largely an academic exercise, because there's no public info on what extra units and functions are available to the GM client, but I think there's a worthwhile discussion to be had on what presentation of information leads to the greatest comprehension and pleasure for the viewer of an arena match.
Please forgive my lack of Photoshop-fu in throwing this together.