Which bosses have an enrage timer and what are their effects?

We already know that the Butcher sets the whole room on fire if you fail to kill him in 3 minutes.

Are just the end-of-act bosses that possess an enrage timer? What are their effects? Is the timing the same for every one of them? Does the timer depend on the group size?

Since patch 1.0.4 Elite packs no longer enrage, and all boss enrage timers only take effect on inferno difficulty.

Boss Enrage Timers

Boss enrage timers appear to be specific for Inferno difficulty only

The Butcher - will set fire to all of the platforms in his chamber simultaneously if you fail to kill him within three minutes.

Ghom - will begin spawning 'Gas Clouds' more frequently after four minutes.

Zoltun Kulle - will enrage, using his 'Ceiling Collapse' ability more frequently, and for more damage after three minutes.

Belial - Enrages after three minutes in phase 3, increasing the number of green pools spawned, which will be spawned across the entire platform.

Cydaea - will enrage after four minutes, causing spiderlings to spawn more frequently.

Rakanoth - will become more aggressive after three minutes.

I've hit enrage timers on Blue and Yellow mobs before. As soon as timer hits, the mobs did instant/constant AOE damage. I was playing on inferno, and the effect was hitting me for 5k dps

I'm not sure of the time it took for these mobs, but I do know it was at least 3 min. I would say it felt close to 10 min, but game time always seems longer. It was a mob of 3, for the record

I doubt these have to do with enrage, but I know that if you haven't killed Diablo within like 2 or 3 minutes he does that colorful purple blast that hits pretty hard. My friend said Azmodan's Hell's grasp type attack starts covering the entire map after 3 or 4 (reported for inferno).