This is a great little game. A simple concept but well executed.
It starts out really slow, but it ramps up at just the perfect rate (and I think the slow start is perfect, because it makes the later stuff feel just that much better); the progression is really nicely tuned. My favorite part of the game is the mid-game where things are flying around and the effect is mesmerizing; it's easy to get into a trance watching the things fly around. Early game things are slow, and late-game when the screen is absolutely filled with balls you lose a little bit of the magical chaos that makes the mid-game feel so cool, because at that point everything is pretty much stationary.
I wish there was an indicator when I maxed out the drag upgrade, and I wish there was more of an endgame instead of just waiting for my browse tab to crash :P Maybe at the end, the screen could zoom out or something so that it's never more then x% full? But then you lose a little bit of the number-go-up feeling if you do that, so maybe not worth the trade.
I also would have liked some more variety in the music (it is nice but it gets a touch repetitive after a while), and some auditory feedback for collisions.
All-in-all, this was a really fun entry. Great work all around!