Almost forgot! Please consider this an "undocumented feature" for the moment, but for those who are feeling brave, the distribution includes the entire python standard library, meaning you can do all types of nifty things, including (as per Jace11's suggestion):
Code:
from random import randint
group.speed = randint(5,9)
group.updateWaypointSpeed()
Which makes the group speed random between 5 and 9 knots. Obviously, all instances of the group will travel at the same random speed
You can use any of the functions described in the python documentation...
(edit to fix problem in example)