I am not sure what your virtualization experience is, but your response "ESX 3.5 is 32-bit, and while it can run a 64-bit guest OS, I wouldn't recommend it" is incorrect. My experience has been different as I have been using VI3 for 3 years ever since ESX 3.0, and it has fully supported 64-bit operating systems, and 3.5 and 4.0 continue to do so today. It has everything to do with the Processor CPU, not the Service Console of ESX.
When you say 3.5 is 32-bit, you are referring to the Service Console which is in fact 32-bit, but it has nothing to do with the hypervisor that runs the guest operating system. The Hypervisor has full 64-bit support. I can understand how this can be confusing because when you SSH into a 3.5 host and do a 'uname -a' you see a 32-bit linux kernel. This is for management purposes only. In ESXi this doesn't even exist.
I believe what the author of this article is saying is "when will VMware officially support these operating systems?". Yes it works on 4.0, yes you can find tweaks for VMware tools for R2 graphics drivers, yes you can ignore the "(experimental)" tag, yes you can trick the OS type by saying it's vista,......BUT this is unacceptable behavior for such a large company who supports such expensive datacenters. Going silent for this long having "experimental" support for an OS that not only has passed RTM but public availability is quite strange. Before 2010 Q1 I would expect to see at least something on the subject.
I Google "ESX 4.0.1" everyday in hope that the next update of VMware vSphere will be available and support all the latest stuff Microsoft has had to offer. One day I will wake up a happy man!
To those that are on edge of upgrading production systems to 4.0 from 3.5 I can tell you this. The ESX upgrade to 4.0 was actually the least painful upgrade I've experienced with VMware (waking up to expired licenses with 3.5 Update 2 was so memorable!) . I recommend using the VMware Host Update utility, placing your hosts into maintenance mode, and using the ESX 4.0 ISO image to do the update. Quick, painless, and so far hasn't caused a single issue with the VMs. Of course you must upgrade to vSphere 4.0 which can be some work, but I have both production and development machines running without any downtime since the upgrade (500+ VMs)