I've been using the Open Source Edition for 5 minutes now *sarcasm..it's been about 3 days* and any review or screenshot can not do it justice unless you install the product. It has been very easy to install and the support forums have been extremely helpful. In the past I've used postfix, sendmail, and tried qmail but none compare to the features and overall install time of Zimbra.
I've already recommended the product to a handful of people and one even suggested that they would purchase the relatively inexpensive commercial network edition rather than using the open source edition. You guys should be proud of the work you are doing.