Thorizdin: Can you give a specific scenario you want to see? That will help us spec the feature out right!
A user should able to see a report based on threat per ability similar to the current Damage Dealt. Other reports that would be good for tanks are mitigation and their source, for example Sonic Barrier provides Juggernauts with a 850 point damage absorption shield. If you look at the logs I uploaded for our last HM EV/KP run you can see that I had the Sonic Barrier effect applied 285 times but I can't tell how much damage was actually absorbed and how many of those shields were "wasted".
A threat over time comparison for all members of a raid would also be extremely helpful so we can see who, and why, is approaching the top of the threat table. This could even be done in the form of a color coded line graph showing the relative threat level of all the members of the raid.