So just the other day I stumbled across this app for the iPad: Maide Control for Sketchup. Basically, what this does is turn your iPad into a giant multi touch controller for Sketchup. I have been playing around with it for a few days and so far it's pretty handy. I have yet to really use it on a hardcore modeling project, I have just been toying around with it.
The app is very well done, and setup is really easy. As you may know, I am a big fan of the 3D Connexion Space Explorer. However, as great as the Space Explorer is, it's not exactly portable. Maide allows you to make a great accessory for Sketchup out of something that you're probably already carrying around. Check out this video to see what it's all about. Maide works on both Mac and PC. If you end up trying it out for yourself, let us know how it goes in the comments.