One of the many 4.0 stories hit the home page of digg tonight.
http://digg.com/linux_unix/AJAX_e_mail_and_more
PS: For those who didn't see their logo in the 'customers' box on the home page, digg (the company) is a Zimbra customer. Good mix of PC, Mac, and Linux desktops with mobile sync needs so a perfect fit for Zimbra's mix of technology.
