So I just was on Stephen Reid's twitter (
https://twitter.com/#!/Rockjaw)
And saw this: Two... guild deployment emails will start going out in a few hours, and they'll be sent gradually over a few hours. More later.
I assume this means that we will be learning what server we will be on at that time.
Of course most Rarity and Fluttershy probably won't be on until they are sent out anyway.
I'll update this post when we get our info.
Also Fluttershy probably will make an official guild announcement of what server we're on.
Edit: also the "two" doesn't mean two emails, it's the second of 4 updates today.