I have found a solution!
Hello there!
I've been looking for exactly this fix for a long while, and have come across your posts several times. I'm a scientist, and read research papers on my iPad, but it's annoying that the zoom changes / the page flies about whenever I brush the screen with my hand, so the ability to lock the input is quite important to me.
After weeks of searching, I've found two solutions, both of which require a jailbroken iPad. I know it's been a while since you posted this question, but I hope you see this post. I'll try and post this reply on a couple of other forums looking for this fix, too. Maybe next time you go on a search, you'll see one of them.
Solution 1: Download a Cydia application called iWhiteboard. This uses activator gestures to enable a 'draw mode' which disables the touch screen as a by-product of it's function: scribbling all over the screen. However, you can enter the 'eraser tool' with a couple of clicks, which is essentially a disabled screen. No touch input will do anything, except the activator gesture to disable iWhiteboard.
Solution 2: This is a better solution, but is slightly more tricky to implement. Finding this took a stroke of genius on my part, I hope the developer considers adding it to a more mainstream repo. There is a repository for Cydia, created by a developer for one single app: "Touch Lock". It's amazing, and is exactly what we've been looking for.
Add the source "http://cydia.myrepospace.com/tomoru84/" to Cydia. The server for this source is really slow, so be patient while it verifies the URL. Next, browse to the repo, and install Touch Lock. You can assign any activator gesture to lock/unlock the touch inputs on an iOS device. It works perfectly on my iPhone (running 4.1), but my iPad is on iOS4.3, so I've not been able to jailbreak it for a test just yet. Hopefully in the next week after Comex releases an untethered jailbreak for iOS4.3.
I hope this helps you (and others) who have been looking for a solution which enables the temporary disabling of touch-inputs on the iPad for reading, passing it around, watching videos etc. Enjoy!
EDIT: Unfortunately, Touch Lock has not been updated for use with iOS 4.xx and likely will not be updated to run on iOS 5 either. iWhiteboard remains the only viable solution that I've found to this problem
