I found this very helpful blog after running into some of these same problems with 2003->2007 coexistance/migration.
I know negative comments do not fix problems, and no disrespect to the Exchange programmers, but I have realized 2007 is an utterly unfinished product. And I am looking at a migration that cannot support the needs of my users within their budget. Unfortunately we already have 2007 running (with test mailboxes only) on the brand new server in the Exchange 2000 organization. So now the question is how to kick this thing to the trash without wrecking the current organization/AD. I am not seeing many articles on going back to 2003 after 2007 is installed...
If I wanted coexistence problems and clients lacking features, I would have just used SendMail and saved $12,000 in licensing.
Sorry to be so mean, but I am really disappointed in Exchange 2007.
Evan