2 weeks ago we hit ZBB. We do some funky stuff to describe the goal.
For example, we only counts bugs that are >48 hours so. Bugs take time to get routed, investigated, etc., so this helps make the problem more tractable.
Then we discount bugs that are blocked. If I can't fix my bug until, say, the Longhorn team fixes something, or we get a new drop of SQL, then we don't count it against ZBB.
The other thing to remember is the the second “B” means “bounce”. That is, bug counts will pop up again after we hit 0.
Tomorrow is 2 weeks from the day we hit ZBB. My hope is that the team will hit 0 again tomorrow. This time, I'm making fewer exceptions. I figure that in the long run, it doesn't matter what's blocked, or newly found, or whatever - when we ship the Beta, that's it.
After we ZB this second time, we're going to a “rolling ZB” mode, where we try to hit 0 bugs > 48 hours, just about every day.
This is the road to shipping.