An Apple tablet won't be thought of or pitched as a computer any more than the iPhone was. It will, however, still include OS X, swanky hardware, an SSD drive, etc. It will be a mini-computer. But to the consumer, it will simply be a magical tablet capable of doing almost everything the average user does.
Check online bank account, surf the web, etc. are a given with Safari. So how about a nightlight/clock/alarm clock? Or an ever-changing slideshow device (which allows you to stream any Apple TV or Flickr or .Mac photos)? Best yet, a true Universal Calendar. This ties to Google Calendars, allowing an entire family to coordinate schedules. School calendars, work vacations, birthdays and dentist appointments all easily retrieved and shared throughout a house.
Form factor will be key, so the tablet will pretty much be about the size of a Kindle, only thinner and more elegant. No orientation. No handedness. Just a gleaming sliver of silver and glass. A TV on steroids. The iHome.