Vmware released Update 1 for ESX4.0 and vCenter Server 4 at November 19, 2009 and is ready for immediate download.
What’s new in Update 1 for ESx 4.0 can be found here : http://www.vmware.com/support/vsphere4/doc/vsp_esx40_u1_rel_notes.html
Support for Windows 7 running as a guest os has been added. Also, vSphere client can now run on Windows 7 without doing some manual adjustments.
In the past when a customer wanted to use Windows Server 2000/2003 Cluster Server or Windows Server 2008 Failover Clustering, either a separate VMware cluster needed to be used for clustered VM’s or the ESX host needed to be disabled for HA. Using Update 1, the VM’s part of the cluster can be disabled for HA and DRS. Also support for VMware’s VDI technology VMware View 4 has been added.
Update 1 for vCenter Server 4.0 adds support for IBM DB2 databases as vCenter backend database. HA clusters can now support 160 virtual machines per host in HA Cluster of 8 hosts or less. The maximum number of virtual machines per host in cluster sizes of 9 hosts and above is still 40, allowing a maximum of 1280 Virtual Machines per HA cluster.
More info on http://www.vmware.com/support/vsphere4/doc/vsp_vc40_u1_rel_notes.html