The SofShell iPad 2 case is compatible with the SmartCover, and as is very tacky as shown in the videos below. This "non-slip" iPad case adheres to a sheet of glass, even when raised beyond 90 degrees.
Here they put the iPad 2 on most flat, and windshielded part on a Porsche going 60 mph. Not sure about this test, without the brake light shielding the iPad 2 I think it would have flown off since the iPad 2 is sort of like an airfoil.
The SofShell is available for $50.