I have to put a lot of iPads on a stantd on a tourist fair to show our web, and we don\'t want that people can use these iPads to play/enter facebook/etc. Is for this that I
Achieveable in software like so: Settings > General > Accessibility > Guided Access
Set a pin if your iOS device has public access.
once in the app you want to lock down, triple click the home button to enable guided access. With this on users will be restricted to your app (or webclip) and required to enter the pin to exit to iOS home if they hit the home button.
Why do you need to block the button? If it's some kind of evil plot to make developers only use the device for developing, the home button IS important: you must test what happens when the real user do that.
Could you not use the parental controls to restrict/prevent access to Safari, Mail app's etc?
On iPad,
Settings > General > Restrictions
You can then easily remove app's such as Safari from the ipad's springboard, and to enable access requires a code (which you set) so no one would be able to access default app's that you don't want them to :)
Of course people would still be able to exit your app by pressing the home button, although they would not be able to do anything, and you can even stop them from deleting apps through the restrictions settings.
The only way to prevent exiting via the home button would be to physical stop people from pressing it by having the stand cover it over.
There are companies that make specific products for this type of thing. Here is a write up a couple (they are not cheap)...
http://www.tuaw.com/2010/04/26/ibracket-turns-your-ipad-into-an-ikiosk/
Steven