I am working on a nightshelter signin application in CiviCRM, and the suggestion is to use a 10" tablet. I'm not sure this would work although the menu is much simplified. (I have a 7" tablet and it would be pretty unusable on that). Has anyone used CiviCRM on a 10" tablet? Was it usable?
The main factor is probably the resolution of the tablet rather than its size, but the UI is in general meant to be used with a keyboard and a mouse (or very very pointy fingers ;)
For the mobiles, they have been several projects to provide a subset of CiviCRM features available.
One is cividroid, an android application from the latest google summer of code https://forum.civicrm.org/index.php?topic=36037.0
Another is an extension on the server that adds a few "mobile friendly" pages https://civicrm.org/extensions/civimobile
If the aim for the tablet is "only" to do the registration, using drupal as the CMS+bootstrap as the theme+webform+webform civicrm should allow you to have a user friendly form tailored to your need that will push the data in civicrm (create the contact, the activity and the case for instance), to be used later with the "full" civicrm from a laptop