<p>I'm using VMware Workstation 6.0 for simulation of tight clusters of "blades" in a "chassis". Both the host and target OSs are Linux. Each "chassis" uses a vmnet switch as a virtual backplane, to which the virtual blades connect. Other vmnet switches are used to mediate point-to-point connections between mutiple virtual ethernet adapters on each blade VM. The chassis, and thus the VMs, are brought up and shutdown rather frequently. My scripts (python) make heavy use of the VIX api, and also manipulate the .vmx config file.<br><br>
What do I gain and/or lose going from VMware Workstation to ESX? Do my scripts that use the VIX api still work? Do my rather complicated virtual network topologies, with lots of vmnet switches defined as "custom", still work the same way? Is the syntax and semantics of the .vmx config file the same between Workstation and ESX?<br><br>Thanks in advance for your help.</p>

The first thing you'll gain by switching will be a substantially more powerful platform that's running directly on the bare-metal of your server.
From my experience, moving
up
the VMware application stack has never been problematic (Server to Workstation to ESX). However, I would verify this by exporting all of your VMs from the workstation install to an ESX install to make sure you're not seeing any 'weird' issues related to running the high-end tool from VMware.
From my [limited] experience, scripts also carry-over cleanly: each offering moving up their product line doesn't break lower-level tools, but do add substantial improvements.