Oct 24th 2008 8:34AM hmmmm ...
I guess it's all a 'your mileage may vary' kind of thing. I'll take your word for the concerns for Metamorphopsis in PvP; not being much of a PvP player myself ... and admit to having the sharpness to have banished a mini-illidan while finishing up one of the Hallow's End achievements. (why no one did it to me in return, now that I don't understand).
In PvE and Raiding, however, my experience has been that Metamorphosis is too much fun to let lay idle; and beside the sheer fun factor it's a significant spike to one's damage output every handful of minutes. The biggest problem so far seems to be psychological; knowing when to stop and bounce out so that you don't take a world of hurt when you lose demon form - which can be hard to see in the middle of an AoE stormfest :)