My impression from Wave was the same: the hierarchical structure turns "waves" into an unmaintainable mess too easily and too quickly. I find the user interface a bit counter-intuitive and cluttered too.

Whatever Paul feels about Wave, he actually makes a couple of clever suggestions Wave's team, I think, should listen to: make it (optionally?) linear and also build the wave-to-email gate. These two things are more important for Wave at the moment than anything else.

If Paul built Wave it'd probably be in a more usable state now, wouldn't it?