Nice article called Coming up with Puzzles about creating 2d avoidance puzzles in Unity3D by the guys creating the game ROBOMINION — a beautiful little game in which you must help a robot to his destination by placing objects in his path.
He talks through the process of wanting to create an algorithmic puzzle generator, but finding that making it work would take more time than hand-crafting 50 puzzles. And then a bit about their process, starting with a blank area, they then balance the levels by hand using some in-editor controls they’ve customized for Unity3D.
They are sponsoring the game on Dentura — go, donate to their cause, it’s only $3.99, download the alpha, and give useful feedback! It’s a great game.