In fact, they claim this rendering from Flickr user Fotoboer.nl is the nearest anyone has come to the actual device.
Some additional interesting tidbits ...
Nestled in an aluminum shell that leverages the Apple's expertise in unibody construction but thinner proportionality than the original iPhone, the tablet reportedly sports all of the same buttons found on the handset, right down to its iconic home button -- which, like the volume toggle, is missing from the rendering.
Similarly, the tablet is said to sport all the same in/out connectivity as the current iPhone 3GS, including a 3.5-mm stereo headphone jack, built-in speaker grills, a microphone, GPS, 3G connectivity and a 30-pin dock connector. Like the rendering, its 10-inch display is framed by a black border that bleeds into its wrap-around aluminum enclosure.