When I am sending an email in Kmail all the recipients in the drop-down box are duplicated. They are not duplicated in the address book itself. In .kde/share/apps/kabc I have std.vcf, std.vcf_1, std.vcf_2, std.vcf_3, std.vcf_4, std.vcf_5, std.vcf_6, std.vcf_7. They all appear identical and without duplicates, though with varying modification dates. When I was using SUSE 10.1 the duplication was evident only for the first email of the session, after that the list was OK, now with Kubuntu 6.06 the duplication persists. This is more an irritant than a problem, but I would prefer to fix it.

No duplicates on my system, but I also have std.vcf_1, std.vcf_2, ... Seems to me that they are just backups.
(Sorry for not being able to provide any more useful info.)

This turns out to be Bug #47919 on Launchpad. The cause was a redundant patch for an earlier bug. If you click on the "select" button when composing, drop down the "address book" listbox that defaults to "all", you will find that everything is duplicated there as well. Select one instance of "resource" or whatever, and the duplicates vanish. The effect persists from session to session, and so solves my problem at least.
I can't tell if the bug has actually been fixed for Edgy, but obviously it has not for Dapper. There is a way of fixing it yourself, it is outlined in the bug correspondence.