Well it goes something like this....

 You cast Balance, I am given the opportunity to counter spell this spell.
You have already paid for the casting cost, and we are in an 'inturrupt
phase'. If I do not choose to counter this spell it is basically considered
succesfully cast.  The spell then goes on to an instant phase, where you
can sac all your land and there is 'pretty much' fuck all I can do about
it. (I can still cast a Indirect (or something like that - the one that
does not let you use an ability))  But you get to sac all your land away
_before_ Balance looks at the amount of land creatures etc.

 Kinda dumb if you ask me, but it seems like we are finding out a lot of
rules like this....

Mike