[This is a copy of bug #234924, which was closed because it was filed for Plasma 4, which is no longer maintained.] The desktop cube effect is nice, but handling the cube feels somewhat artificial. What I think would help is giving the cube some inertia. A demonstration says more than words. To see what I mean, download and run the game FooBillard. When the game starts, click and drag to rotate the billiard table. When you let go of the table (at moderate to high speed), it continues to rotate for a little while, i.e., it has a somewhat realistic deceleration effect. My wishlist is for this effect to be added to the desktop cube. If you rotate it at high speed, it will continue spinning for a while (not very long, and not a long distance) before coming to rest. If you rotate it at low speeds, the effect should be very subtle.
Sounds less usable, that's the only thing that matters