Thought I would throw this out - Shimon has been great but cannot close this issue.
600, running native Mail app retrieving gmail.
2 day indicates that I have 1 (actually 2 now) email unread. I don't. There is no unread email anywhere on my treo (unread, deleted,outbox,etc) - checked my snapper folders as well just to be absolutely sure.
Shimon suggested an idea (from another user) that had me delete the email account in Mail and setup it up anew. That worked...for about 2 days and then the phantom email showed up (actually it added one - now I have 2).

I could delete and re-setup again but that seems like a never ending battle.
I could delete (using filez) the file that holds the emails if I knew what it was (assuming that if I delete, it will recreate - I don't keep any gmail emails on my treo so blowing it away isn't an issue).

Ideas? suggestions?