Flash Player is somewhat underpowered in terms of computational and animation speed. Therefore, processor-intensive applications, such as 3D, are problematic in Flash. Flash doesn't include any native 3D ActionScript commands or 3D hardware support, unlike Macromedia Director (which supports the Shockwave 3D format).
However, good design is all about knowing the system, working within its limits, and hacking around the obstacles with a bit of lateral thinking or by simplifying the problem. Regardless, while being able to rotate and zoom a 3D model of a wristwatch before you buy it is cool, most customers are more impressed by good 2D photography and proper graphic design in the product presentation.
You can best use 3D as a part of other applications, rather than as the entire application. For example, you can mix 3D animation with traditional animation that relies on the drawing ability of the animator to imply 3D. For a good example of mixing 3D and 2D animation, see the Flash cartoon "HitchHiker Part Two" at Bitey Castle (http://www.oohbitey.com/hh2Window.html). The car animation was authored with Swift 3D (http://www.swift3d.com), then superimposed on the 2D background animation.
Most modern operating systems include faux 3D effects in their GUIs, and you can create faux 3D windows and buttons in Flash. Sites like layerbit (http://www.layerbit.com) take 3D effects to the extreme. The Volkswagen UK site promoting The Phaeton (http://www.thephaeton.co.uk/universe), however, is a more subdued example of scripted 3D that pushes the limits of what Flash can produce in real time without exceeding them.