Awesome, just what I was looking for! Thanks!
One problem with this, though: If you want this to be run for each new object created, it doesn't let you create a certain type of object and then have the function that deals with the family as a whole still only work with that one new object. It would let you do this if the function just dealt with one object type, so it's strange that you can't do this with families unless you want a random object from that family to be created each time.
I'm pretty sure this is just how the object picker thing works, but it's still pretty weird.
I suppose you can create a variable and loop through them all looking for objects with that variable set to 0 or something, but that's kind of a weird way to do something like this.. (An On Create event or something would be pretty nice and solve quite a few problems like this, I think.)