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Other than that, I can't think of why you would have been dropped. If the site topic is still the same and the listing was in the appropriate cat to begin with, then the listing should have stayed.
[edited by: Brett_Tabke at 4:22 pm (utc) on Aug. 18, 2002]
DMOZ has a spider the flags 404s and other site down problems. It may have gone through on a day that you were shifting servers or down for maintenance... If so, you may have been removed. It shouldn't be a problem to get relisted though.
Email the editor, as you planned, then wait a few weeks. If you don't hear anything, move up to the next category and email that editor. Keep doing this until you reach someone that answers. (And remember to be patient...I know it's frustrating, but those folks are volunteers...)