The demo was a lot of fun, but it inexplicably ran like shit.
8800GTX on 185.85, max settings (which includes like a whopping 4x fsaa). I think it was like smoke or particular lighting effects that were bogging down the frame rate, as it wasn't a constant problem.
Whether it's worth $30 will depend entirely on its length, and whether or not the game manages to stay fresh throughout. The demo gives me the impression that the game will not be able to vary gameplay mechanics enough, and the puzzles are a far cry from thought provoking. It's not Portal, and it's definitely not Braid in that regard.
Steam + PSN: PHJF