That forward-and-backward navigation works as you expect, but that also makes up the sum of the Cube's presentation-specific features. It can't control the mouse cursor midair, it can only scroll by the page-length, and there's no built-in laser pointer.
You might not be bothered by any of those limitations. I've sat through plenty of mindless PowerPoint presentations that barely demanded the presenter have a pulse, much less an advanced input device.
If you're happy to settle for the Cube's spare functionality, consider its price in relation to that of other presentation mice. HP, Iogear, and others all offer presentation mice with laser pointers built-in for less than the Cube.
None of those devices matches the Cube's visual appeal, it's true. But they're also big enough to work as respectable mice. My hands are not overly large, but I still found the Cube too small to use for basic cursor control over an extended time period. The Cube's dimensions might make it an appealing airplane mouse, but its size prevents a sure-enough grip for precise spreadsheet work, or anything beyond basic navigation.
As a basic presentation device, and a basic mouse for use in short bursts at a podium or in a meeting room, the Logitech Cube is a fine accessory, if a touch overpriced. You might also like it simply because it's eye catching, or remarkably portable and unobtrusive. It would be an easier recommendation at $60. For $70, I'd like the Cube to do more.