SketchUp Mobile Viewer is the latest product from the makers of SketchUp, and allows SketchUp models to be viewed on iPad, by uploading them to the 3D Warehouse, from where they can be viewed. There are other solutions for exporting SKP files to be viewed on the iPad, but they all require some kind of plugin, and while some of the viewing apps are free, the export plugins are often paid. At $9.99, this is the cheapest way I can see of getting a SketchUp file onto your iPad. Unlike Autodesk's Formit, this is only for viewing, not drawing models, on the iPad.
The first time you download it, you'll be asked to log in with your Google account. If you have uploaded any files to the 3D Warehouse using that account, they'll show up on your home screen. like this:
Selecting one of the files will let you download and open it, and you'll be able to navigate by swiping, panning and pinching to zoom. You can also swipe up the red Warehouse icon in the bottom left corner to open a search window that will show you files from other users on the warehouse.
The 'i' icon contains the model information for the file, and the camera icon contains the standard orthographic views as well as any saved scenes for the model. Unfortunately, section lines and object visiblity don't reflect in this version, but hopefully these features will come in a later version. There is also reportedly an Android version on the way.I tried the app out the other day while building our T-Rex project. I will mention one problem I found with the app- if you have an older iPad with 512mb of RAM, (1st gen mini, or iPad 1 or 2), you will get frequent warnings about running out of memory. Closing all apps and re-starting will solve this for most cases, but very large files might not be able to be opened on your iPad.