I'm sure this may have been answered already, but I can't find anythign definitive.
Zimbra represents a very interesting solution, but the scale of users required to make it worthwhile make it impossible for small business/home users to achieve somethign very important.. offline sync.
Whilst the web interface is incredibly powerful, there are times when you simply dont have a network connection. I work in a very small development team ( < 10 ) users, but there are at least three regular travellers who absolutely rely on outlook to keep a local copy of their email, and to be able to respond to emails and resync when they are next back in coverage.
The Network Version, even at Small Business level is complete overkill, yet the Outlook connector is critical. Could you not employ pricing strategy similar to Ximian and sell licenses per-connection additionally? In this way, users of the Network Version can have a full Zimbra subscription, and also enjoy a rightofuse for the Outlook Connector. The rest of us who simply want a very very low user number of connectors could opt to use (albeit unsupported) the OSS version and just buy 3 or 4 Outlook Connector licenses at , say, $25/go.
In this way, you allow companies like mine to experience Zimbra, to use it everyday, and to develop extensions so we can integrate our existing middleware apps into it - most importantly winning you over the large scale corporate customers required to make the subscription model work. We can't recommend what we can't use day-to-day!
Cheers, and sorry if this has been covered millions of times already.