On the Hello World drawing, some letters are perfect, but portions of some letters are right-shifted a few millimeters (e.g., the inner circle on a letter "O" ). Sometimes there are jaggies.

I've seen the troubleshooting section on 'choppiness.'
--triple-checked the motor hookups
--diddled with the current pot, even including real-time diddling to find the sweet-spot..
--latest firmware, as of a couple of weeks ago.
--the sound of the motors seems okay
--many tries, not one fully successful print of 'Hello World'

Any ideas? Thanks. Easter's coming soon!

What you are describing sounds like the most common sort of Eggbot issue, which is poor alignment or poor coupling between the egg and the motor. Please read carefully through our section on "improving precision": http://wiki.evilmadscience.com/Improving_precision, which goes through a number of things that you should check, and in particular the suggestions in the section called "Check contact."