> Would a good locksmith know how to correctly cut a key when all he has
> at hand is a worn one?

Depends on how worn the key is. There are 7 cuts on the key, with four
possible depths for each cut. A fifth or sixth generation copy cut by
a hardware store goon ten years ago could be nigh impossible to gauge
accurately. The key the PO of my van gave me was such an astoundingly
bad one that I had to pull the door handle to get the number. If
you're going to go through the trouble to have a code cut key made,
it's probably best to get the door handle code in the first place.
Gauging a worn dupe has too much room for error.

If you have the 4 digit number off a door handle, I can cut a key for
it and drop it in the mail to you for $5. It'd be on a generic brass
key blank rather than the fancy plastic headed steel OEM Witte blank
like Steve has (I wish I knew where he gets 'em), but it'll be
properly cut at least.