Didn't settle on anything yet, but have tested SOGo, Zarafa, SmarterMail, MailTraq, MailSite, hosted Rackspace Exchange. Each have pluses and minuses for what I'm looking for.
Some of these run on windows server, some on linux. The linux platforms for testing are SME8b5. My personal like is Zarafa over SOGo for the web interface. The most difficult thing about all this is evaluating one product that will sync with blackberry, smartphone, funambol, outlook, and now Ipad.
If people are interested I can post results when I make a final decision later next month.