You might think im crazy and wonder why i would do something like this, but progressing through Inferno it is not an ability i can use any more. I would love to have the damage boost from it, but there are too many drawbacks:
(It is worth mentioning that i play in 4 man groups 90% of the time)
1. The cooldown
The cooldown has to be there or this spell will be too OP. However when we are fighting elites in Inferno i get no kills in archon form and it ends after 15 seconds. The cooldown means i get to use it once per elite fight.
2. No OH-F**K button
In my build i use wormhole teleport, illusionist and diamond skin to GTFO when !@#$ hits the fan. If i am in Archon form i cant escape when i get ambushed by mobs. In inferno, %^-* hits the fan all the time so it is actually unusual that i get to use my archon for the full 15 seconds. I usually die long before that.
3. It occupies a spell slot.
Occupying a spell slot with a spell that is on CD most of the time seems like a sacrifice that is not worth it.
Whenever i play in normal/NM/hell i will use this ability. It is awsome, and epic fun.
If however blizz could give you your normal abilities, but a buffed version in archon form it would be much much more viable for Inferno.