Possible Input method -- press and drag

[Derek Pressnall]

I've had an idea for a novel input method that would work on touch
screen devices.
The idea is to present a graphic that is similar to a standard phone
keypad layout, with standard lettering and number positions.  To enter
a specific letter, you touch the button associated with that letter
and drag your finger/stylus in a particular direction to indicate
which letter to choose. For example, to enter an "a", press the number
2, then drag to the left and release.  A "b" would be "press 2, drag
upwards and release", and a "c" would be "press 2, drag right then
release".  And so on.  To enter the number 2, just press and release
without dragging.  To be easily usable, the method shouldn't require
you to drag completely off the button, but should also require a
minimum drag length.

What does everyone think about the usability of this type of method?
Once I get up to speed on GTK programming, I can take a stab at it,
but it may be a bit before I get time for it.  So if someone else
wants to give it a shot, go ahead.

--Derek