Cubify.com is running a contest that provides you with a great opportunity to push the limits of the Cube and to show off your work.
It's the Cube Test Print Contest
One of the sentences that is important; but, easily missed, is that the Cube prints in ABS plastic. So, what does this mean for a designer?
First, your design should look good in a single color. Secondly, I'd suggest designs that have details and features at around .5mm or larger. This is an extrusion printer. And, while the detail can be quite good, very fine extended features might be a bit tough to print perfectly.
Based on my experience having a RepRap and examining the Cube, you are going to be very surprised by the quality of the print.