I'm about to search for a bugzilla entry for this, since my co-worker just tested importing (via Outlook 2003) a PST archive he made yesterday. It synchronized the e-mails to the Zimbra server, but they were all dated at the time of import, rather than the YY/MM/2006 they should have shown up as.
We are planning on having end-users run a PST export to clean out some of their hideously large mailboxes, and drop the PST file onto a different file system, but now our fears are they'll try to import it. We have to fear the worst, right?

Anyway, trying to re-export or delete all the mails imported via this method doesn't seem like a fun task to tackle.
If someone knows of the bugzilla # to reference, could they post it here? If there isn't one, I'll open up a ticket and toss it in here.
--Brian
Edit: Found Bugzilla entry:
Bug 25770 – Wrong Time and Date when importing PST file through Outlook