We´ve been using Zimbra since a couple of months now, and I think it´s a fantastic opportunity for each small or medium enterprise, especially when virtual teamwork becomes more and more important (like in my working environment), to make a step towards Web 2.0. Besides typical features a collaboration suite usually offers, Zimbra comes with a couple of concepts which have the potential for a “Next Generation Collaboration” (collaborate or collapse):
- Zimbra comes with a powerful search engine based on Lucene
- Zimbra has an integrated tagging-system
- Zimbra´s spam filter learns from each user in the system, if an email is spam or not – a very good example for an application of collective intelligence
- Zimbra´s Zimlets support meshups and with that mechanism any message content can be made “live” by linking it with other services and content (eg. if in a textpassage the word “today” appears it will automatically be linked with your calendar entries from “today”)
And: Zimbra can be synchronised with your PDA… 😉
About the Social Semantic Web 
… and you can adding RSS feeds as easy as creating a new folder (like your own words! ) 😉