Limitless Solutions' recently released SightSpace 3D app allows you to view SketchUp models on the iPad, iPhone, or iPod (Android support coming soon).

From SightSpace 3D:

SightSpace 3D enables mobile viewing of Google SketchUp designs. With Augmented Reality capabilities, it overlays digital models on the physical world. As a Google SketchUp or Google SketchUp Pro user, use SightSpace to:

• Experience a state-of-the-art mobile Augmented Reality engine
• View Google SketchUp models
• Make your model mobile

Initial reviews comment that orbiting a SketchUp model with single finger, panning with two, and pinching to zoom in and out is very satisfying. Loading models onto your mobile device is easy too; the Google 3D Warehouse is integrated in the app and you can also load models through Dropbox and email.