I've been 'training' on the old FTB SSP map. I notice that on a given day, my first tree tends to grow at about the exact same time within that day. The next day I get a different, but consistent (within the length of 24 hours) growth time. I use a MacBook primarily and often use Bootcamp to load Windows and I notice that the behavior of the old FTB map's tree spawning on OSX differs from that on Windows, though on either platform it is consistent. This leads me to believe that the PRNG is based on the date and also some other characteristic of the operating system beneath the simulation.
So, it's very possible (by my lame, casual observation in my own play sessions) for users on Mac to have an advantage over PC users, or vice-versa. Given the wildly exponential nature of FTB SSP (v1) a player able to spawn a tree very early in his session will have a vastly better opportunity compared to a player using an equally effective strategy whose tree popped 4 minutes later. Do you have a plan for this situation? Will you run separate brackets for users on Mac / PC? Am I simply imagining this 'regular' behavior of PRNG in Minecraft?