I've been having a lot more discussions lately about the very real possibility that HyperV or XenServer may be getting to a state where "good enough" is worth the cost savings associated with these Hypervisors. A large part of me agrees with this, compared to where XenServer or HyperV started, they have made huge inroads on their hypervisors. Also, these two hypervisors are much cheaper than ESXi, so the conversation is definitely worth having. The fact is we are getting very close to a point where we could become hypervisor agnostic.
Over the years virtualization admins have come to expect a lot of very cool features. Something like vMotion was super cool when we first saw it but now we expect it and as such all the hypervisors can do this. Storage Motion is another one of those expected things, and this is where we start to see some advantages in the VMware product. The ability to move storage between local datastores does not exist in XenServer, not something you often need but its nice to know its there when you go to use it. Or how about a simple operation like deleting a datastore (or storage repository in the Xen world). In Vmware you just right click and delete a datastore. On Citrix... well...
The argument that fans of XenServer will make is that this isn't that difficult. They are right, its not. But its a heck of a lot more to keep stored in that brain of yours than just right clicking something and deleting it (never had to Google that). And the fact is virtualization admins just want things to work, very few admins out there today focus solely on the hypervisor, so when they go to work on it they want it simple and they don't want the stress of having to remember how to do basic operations.
Outside of usability, VMware has countless other bells and whistles, most of which you don't need on a daily basis, things like Host Profiles are great when you need them, but if you don't have them you can just manually setup your hosts. So while VMware continues to innovate new technologies, I don't think they've come up with anything lately that is a "must have" technology like vMotion of Storage Motion. As HyperV and XenServer catch up to the "must haves" I think we will start to see a change in the hypervisor landscape.
Do I think we are there yet? No. But I don't think it'll take much longer for Microsoft or Citrix to catch up.