VMware has released a draft of the vSphere Hardening Guide, and are encouraging feedback from the community.  It is broken into multiple pieces.
Part 1: Introduction
Part 2: Virtual Machines
Part 3: Host
Part 4: vNetwork
Part 5: vCenter
Part 6: COS

VMware has released a KB with a handy vmfstools command to check your VM’s disk status.  If the VMFS output shows a “Z” it is Zerothick with blocks that have not been written to yet.
Read the article here.
This allows you to check the disk status for options such as Fault Tolerance or Microsoft Cluster Services.  [...]

If you are looking to update your ESX4 hosts to Update 01, don’t look in Update Manager.  VMware has removed the update because of a bug with the HP Management Agents preventing the update from completely successfully and rendering the host inoperable.
From KB1016070:
“Note: If you want to install the update, you must download the update manually. [...]

VMware has posted a bug when upgrading ESX 4 to Update 01 with HP Management Agents running.  (ESXi is unaffected)
You may have your host end the update unsuccessfully, and in a non-responsive state.  To avoid this, disable all the HP Management Agents prior to running the update.
Read the full article here.

VMware has acknowledged an issue that we have been battling for some time with a Pegasus CIMSERVER memory leak.  It has been fixed under ESX 4, as it does not use Pegasus, otherwise setup a CRON job for restart Pegasus periodically.
This issue has been extremely frustrating in our environment for a very long time, and [...]

Simon Long of The Slog has posted a VCP vSphere Practise Exam built out of VMware documentation and personal information and experience.  Looks great, I plan on taking it tonight to brush up!
Take the Exam here.
VCP vSphere Practise Exam

VMware has released a new white page on memory management techniques within ESX/i 4.  The previous version for 3.x was a great resource for many discussions, troubleshooting, and designs over the past few years.  This new document is every bit as good, but has even better documentation and examples with greater technical information.
Read the whitepaper [...]

You will find these instructions in other How To posts and links here, but I thought I would post a simple KB from VMware for quick reference.  service mgmt-vmware restart, will NOT cause a Guest to reboot or go down.
Click here for the article.