i like 0.6, the "sand box" (i.e. 0.3 or lower) is pretty much all i used so far, i liked the levels, but once you've done the 5-6 levels a few different ways, there's not much more left. i like the use of shake to reset, and the accelerometer as gravity, but it's a bit slower than 0.3, so i'll stick with that for now.
what i would like to see is the ability to change the size of the balls when tapping, eg. the longer you tap, the bigger the ball.
great work though, i look forward to seeing more updates!