Edit: Reading the messages again, and this time pondering along the way, I got the impression that Petrucci and Co. already have a drummer in waiting position. What do you guys think ? 
Nicky.
I don't think so, though they must already have a short-list by now.
I think that the rest of the band, though they probably saw it coming was still surprised.
Mike was struggling with it for over a year, I'm sure as friends and band-mates they felt it too.
I don't think it is a hasty decision of both of them, the band and MP.
DT wanted to move further, Mike couldn't. How hard it might be.
Though I always thought that Dream Theater as a band would split up in it's entirety, or maybe the retreat of let's say either James or John Myung (I always felt that the main force in DT are Mike, John P. and Jordan Rudes), I
never could've guessed that Mike Portnoy would be the first one to throw the towel in.
I respect his decicion to leave the band on his terms, in good harmony and friendship before anything would blow up in their faces.
It's a brave way to leave the building like that.
Especially for someone who's been the engine (together with John Petruci) of DT for so long.
On one hand I'm thrilled that the band already pointed that Black Clouds won't be their swan-song but on the other hand I'm afraid that something bad will come out of this.
There are a lot of doom thinkers (is this correct in English?

) on this planet but the story that was posted by Tom doesn't bring me good vibes in my system.
Maybe (and hopefully) I'm too negative about this.
But somehow these negative thoughts keep roaming my mind.

But ... let's brainstorm about this.
Dream Theater without Mike.
Who could possibly become the new drummer of Dream Theater?
In the past few days I've heard a few rumors or suggestions about who the new drummer would or should be. (how strange this would seem but life does go on).
Funnily enough, the name that you could hear the most was...Nick D'virgilio. (Spock's Beard anyone?)
No doubt in my mind that he is a great drummer and would probably easily fit the melodic Dream Theater but he's not a metal kind of guy.
More a prog rock drummer.
He could always do the drums for the record and then Dream Theater could go on tour with a different drummer, especially for the metal-stuff but somehow I don't think that that would fit in Dream Theater's agenda.
They aren't the kind of band that hire one man for the studio and hire a different man for the tour.
I know, in retrospect Derek Sherinian was what you call a hired gun but the band only recruited him because Jordan was working with the Dixie Dregs on that time.
But...maybe I'm way off on this ...
What about Mark Zonder? (<---formally the drummer of Fates Warning)
Besides the fact that he's a superb technical drummer, he also has the 'metal' touch.
I know he has his own band/project right now (slaviour) but to my knowledge it doesn't really do what Mark hoped it would do.
To me he would fit quite well.
What do you guys think?
In fact, come to think of it, as a drummer (not as the engine of DT) it might be quite easy to replace Mike.
Let's face it, though he is an excellent drummer, he is not the only one that can chop the sticks that way.
In fact, go surf through Youtube and you can see a lot of so called amateurs who record whatever cover of DT they are playing. And most of the time they do that quite well to say the least.