Thanks Charles, for posting your solution! It took me a couple hours trying to find this solution and the LiveScribe link here solved a similar problem I was having.
I had a "ghost user" living in my SL 10.6.8 MBP that I wanted to remove so I could re-use the name (and not have any leftover user accounts that the system was holding onto.) The old user I thought I had already deleted was revealed by Easyfind and showed up in Applejack as a user while in sudo mode, as Applejack allows you to choose which user prefs you want repair and caches you want to purge. I don't use Terminal much but it was very easy to delete the ghost in the machine by copying and pasting--in case someone else has the same issue here's what did the trick:
sudo dscl . delete /Users/GhostUserNameHere
You must use the exact [short] user name, case sensitive. It took me three tries because I left a space or incorrect cap usage, or used the Full Name which was very similar but capitalized differently. If you're inexperienced with Terminal it's important to remember you can completely screw yourself if you make a mistake so don't change anything before the last "/". Hope this helps someone!