This may be old news, but I found that by playing with a trackball, when you get the grab-paddle/catcher's mitt power up, and then catch the ball in the exact middle of the paddle, it will shoot straight up from that point on. It works because with a trackball, you can keep the paddle absolutely stationary between the time you shoot the ball and the time you catch it (something much harder to do with a mouse); and as long as the ball stays in the exact center of the paddle, it keeps shooting straight up. This allows you to roll the paddle back & forth, aiming shots with great accuracy. It also makes 'cracking' the unbreakable bricks a lot easier because the player can keep hitting one over & over.
The only problem is, at rare intervals, the game will 'cheat', and kick the ball out at something other than a 90 degree angle. But until then, you can catch the mini ball, fast ball, and mini paddle power ups and rack up a good score on the board.
Any other hidden tactics or strategies out there for DX Ball2? (I purchased Rival Ball, but don't care for the smaller bricks).