Scalix is a good product .. Its not Zimbra .. we have also deployed and own lic for Scalix ..
Yet one more product to look at is
http://www.open-xchange.com/ it came from OpenExchange by SuSE and was and still is a great product .. Note they have also come a long way with Outlook integration and also support BlackBerries ..
Now that said I would not say I am saying to jump the Zimbra ship yet but we all need to keep a close eye on the following few months to see where MS goes and just how willing Yahoo is to give up to Google and sell out.
BRW