The NY Times reports:
"... another recently departed Apple employee tipped me: 'You will be very surprised how you interact with the new tablet.'"
http://bits.blogs.nytimes.com/2009/12/23/2010-the-year-of-the-tablet/
So what are the ways one can interact with a tablet computer?
-- a physical keyboard attached by Bluetooth
-- an on-screen keyboard using fingers or stylus
-- printing or writing on the screen, which the computer translates to text
.. a stylus would work better than a finger for writing
-- making "gestures" on the screen
.. Palm Computing's Grafitti language is one example
.. new capacitive displays allow multi-touch (commands using more than one finger at a time, like pinching to make an image smaller)
-- voice recognition ("I'm sorry Dave, I'm afraid I can't do that.")
-- accelerometers that detect motions of the tablet (shaking, turning, etc)
EDIT
Two additional ways to interact with a slate computer:
Pressure sensitive touchpad
Imagine a touchscreen with many more levels of sensitivity
to pressure than the typical touchscreen. Wacom makes this sort
of touchpad for graphic artists.
Swype keyboard.
Instead of tapping on the virtual keyboard, Swype enables you to
trace a path over the keys without lifting, starting at the first letter of
the word, and lifting when you reach the last letter.
The Swype program uses a dictionary to make intelligent guesses
about the word you were trying to enter. Multiple languages are
supported.
This sounds impossible, but it works! Swype claims you can learn
to enter 40 words per minute on a cell phone virtual keyboard.
Check Swype out here
http://www.swypeinc.com/
To see a novice user learning Swype
http://jkkmobile.blogspot.com/2009/12/testing-swype-for-android-on-motorola.html
There is a version of Swype for Windows Mobile phones, and
just released for Android.
Any other input methods?