A user tip , submitted by:

Here is a tip for your Handheld User Interface Ten Commandments
(http://www.fo.com/articles/mc-01.htm) article, 


If you are designing an application that you particularly expect will be
used in an airplane (or vehicle), make it forgiving of shaking hands. 
(an old tip from Apple HI people for laptop design).

   This may imply:

    a) larger target (tap) areas,

    b) extra Undo or more acknowledgement dialogs,

    c) more tolerance of sudden jerks of the stylus if there 
       is a drawing aspect, effectively running a smoothing 
       algorithm.

       Maybe even a special (moving) mode is needed?

Seconding the tip about using thumbs ("Thou Shalt allow Chubby Fingers to
Operate a Touchscreen") -- remember the poor soul who just lost their
stylus and don't trap them without being at least able to finish an 
operation without one (ie: if there are important buttons to press make them 
fingerable).

Tip #1 ("Thou Shalt use only a Couple of Fonts") applies even more so if your
target audience is aging or people with illness affecting motor control.