On the "Product Z" launch level where you blow up the building, my wife (who'd managed to get that far easily enough) kept on releasing only one of the balls at first which results in a bug that makes the level unpassable.

If you only release one of the three balls, they then float up the pipe to the top of the building by themselves. Once you've seen up the top, the camera then won't let you go back down to release the other goo needed to blow the rest of the roof off. You end up just blowing up the top part, and never being able to release pretty goo# 2 and 3.

I watched her do this repeatedly getting more and more frustrated. I'd suggest making it that the camera always lets you move to where the pretty goo balls at the start are stored so people can at least see where they went wrong.

World of Goo rocks.
That is all.

doesn't happen that way for me.  I can move the camera down there no problem.

but... this could always be looked at as a "feature vs bug" debate.  It's meant so if you DON'T release all three balls you can't win!

But again, I released one, followed it up, built up to the match, blew stuff up, then went down to the remaining two balls, all with no problem.

with this one... start at top and work your way down so all three balls go up at the same time...
if you remove a green goo from the top row, then a green goo from the bottom row you get:
o
o
_
o
now throw one of the remaining goos onto one of the top balls which forces the third row to snap and all the balls fall (it just saves a move if your interested in that and takes all three balls at the same time)

Or just remove all the goos from top to bottom so they all go at the same time... then you dont ever have to worry about going back down.