It has been known for quite some time that Yahoo are trying to make bold changes internally. Products have been shut down (eg. Yahoo Live and Geocities) and it has been rumored that Zimbra has been up for sale for quite a few months by now.
If VMware ends up acquiring Zimbra it’s a very strange deal, but it might make sense. With VMware’s virtualization expertise, they might very well be able turn Zimbra into a powerful virtual appliance. That could work both sell it as a software appliance (just the virtual machine) as well as a hardware appliance (hardware). Combined with VMware’s virtualization product line, they can target everything from small business (VMware Server) to large enterprises (ESX). This could be a very serious threat to Microsoft Exchange.