I was really disappointed (and so were several other members of the community) when I found out that VMware had purposely pulled support for ESX as a host because I knew that a lot of people relied on the ability of running ESX in VMware Workstation for testing purposes. Check out this website by fellow Dutchman and VMware guru Eric Sloof for the details on running ESX on VMware Workstation 6.5 Beta 1 Refresh.

This renewed support for ESX is of course an "unofficial" new feature in VMware Workstation 6.5 Beta 1 Refresh. The official list of new features is:

• Performance enhancements to VM Record and Replay — Enjoy faster performance with our advanced VM Record and Replay technology. Record your entire VM execution and replay it with instruction-exact precision. A graphical interface lets you browse, add markers to and edit your recording so you can easily monitor and analyze your virtual environment.
• Unity for Linux Guests — Enjoy seamless integration of your favorite Linux guest applications with your host. You can launch, access and run guest applications alongside host applications! Unity for Windows Guests is already supported in the previous VMware Workstation 6.5 Beta release.
• Easy Install Option for Linux Guests — Save time and simplify Linux guest operating system installations with the Easy Install Option.