VMware ESX 4.0, Patch ESX400-Update01
From the release notes:

VMware View 4.0 support – This release adds support for VMware View 4.0, a solution built specifically for delivering desktops as a managed service from the protocol to the platform.

Windows 7 and Windows 2008 R2 support –This release adds support for 32-bit and 64-bit versions of Windows 7 as well as 64-bit Windows 2008 R2 as guest OS platforms. In addition, the vSphere Client is now supported and can be installed on a Windows 7 platform. For a complete list of supported guest operating systems with this release, see the VMware Compatibility Guide.

Enhanced Clustering Support for Microsoft Windows – Microsoft Cluster Server (MSCS) for Windows 2000 and 2003 and Windows Server 2008 Failover Clustering is now supported on an VMware High Availability (HA) and Dynamic Resource Scheduler (DRS) cluster in a limited configuration. HA and DRS functionality can be effectively disabled for individual MSCS virtual machines as opposed to disabling HA and DRS on the entire ESX/ESXi host.

Enhanced VMware Paravirtualized SCSI Support – Support for boot disk devices attached to a Paravirtualized SCSI ( PVSCSI) adapter has been added for Windows 2003 and 2008 guest operating systems. Floppy disk images are also available containing the driver for use during the Windows installation by selecting F6 to install additional drivers during setup. Floppy images can be found in the /vmimages/floppies/ folder.

Improved vNetwork Distributed Switch Performance – Several performance and usability issues have been resolved resulting in the following:

Improved performance when making configuration changes to a vNetwork Distributed Switch (vDS) instance when the ESX/ESXi host is under a heavy load
Improved performance when adding or removing an ESX/ESXi host to or from a vDS instance

Increase in vCPU per Core Limit – The limit on vCPUs per core has been increased from 20 to 25. This change raises the supported limit only. It does not include any additional performance optimizations. Raising the limit allows users more flexibility to configure systems based on specific workloads and to get the most advantage from increasingly faster processors. The achievable number of vCPUs per core depends on the workload and specifics of the hardware.

Enablement of Intel Xeon Processor 3400 Series – Support for the Xeon processor 3400 series has been added.

ESX 4.0 Update 1 requires a host reboot and VM shutdown.

Note that several of the upgrade methods that were available with past ESX editions are not available. These include the GUI or text mode upgrade from CD, scripted upgrade from CD or PXE boot and upgrade with a tarball via the service console. Only the vSphere Host Update Utility and VMware Update Manager are supported for performing upgrades from ESX 3.x to ESX 4.0 Update 1

Cisco Nexus 1000v
VEM-4.0.0-update01-v100

VMware vCenter 4.0 Update 1
From the release notes:

This update release of VMware vCenter Server 4.0 Update 1 offers the following improvements:

IBM DB2 Database Support for vCenter Server — This release adds support for IBM DB2 9.5 as the backend database platform for VMware vCenter Server 4.0. The following editions of IBM DB2 are supported:

• IBM DB2 Enterprise 9.5
• IBM DB2 Workgroup 9.5
• IBM DB2 Express 9.5
• IBM DB2 Express-C 9.5

VMware View 4.0 support — This release adds support for VMware View 4.0, a solution built specifically for delivering desktops as a managed service from the protocol to the platform.
Windows 7 and Windows 2008 R2 support — This release adds support for 32-bit and 64-bit versions of Windows 7 as well as 64-bit Windows 2008 R2 as guest operating system platforms. In addition, the vSphere Client is now supported and can be installed on a Windows 7 platform.
Pre-Upgrade Checker Tool — A standalone pre-upgrade checker tool is now available as part of the vCenter Server installation media that proactively checks ESX hosts for any potential issues that you might encounter while upgrading vCenter agents on these hosts as part of the vCenter Server upgrade process. You can run this tool independently prior to upgrading an existing vCenter Server instance. The tool can help identify any configuration, networking, disk space or other ESX host-related issues that could prevent ESX hosts from being managed by vCenter Server after a successful vCenter Server upgrade.
HA Cluster Configuration Maximum — 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.

vCenter Server 4.0 Update 1 includes updates to VMware Converter Enterprise, VMware Update Manager, VMware Guided Consolidation and VMware Orchestrator

VMware Data Recovery 1.1

The following enhancements are included in Data Recovery 1.1

File Level Restore Functionality is Officially Supported
File Level Restore (FLR) provides a way to access individual files within restore points for Windows virtual machines. In previous versions of Data Recovery, FLR was provided as an experimental feature. File Level Restore feature is now officially supported.

Integrity Check Stability and Performance Improved
The integrity check process is faster and more stable. Note that integrity checks are computationally intensive processes and can take significant periods of time. The exact amount of time integrity checks take varies based on of the size of the deduplication store. Even with these enhancements, integrity checks that take several hours are not unexpected.

Integrity Checks Provides Improved Progress Information
When an integrity check is running, a progress indicator is displayed. This progress indicator has been improved, although it does not provide the optimal level of detail.

Enhanced CIFS Shares Support

Patches are available on the downloads page.
One of the locations that VMware lists updates is on the VMware Knowledge Base Blog.