Marathon Technologies have released their everRun product for Citrix Xenserver which adds HA/ Continuous Availability to Xenserver. Have a look at the picture:
The first thing I notice is that this clearly hasn't been written by someone who sells SANs. There is no requirement for shared storage; this is great for lower cost implementations. Basically if one physical piece of hardware fails the machine continues running on the other host, this is the big brother of HA: Continuous Availability. This is going to put a fire under VMware to release their pre-beta Continuous Availability feature.
As you can see the eveRun bit insinuates itself between the Hypervisor and the VM, intercepting calls and replicating them to the partner, what the performance impact is if any I don't know. It's doing basically the same thing as VMware wants to do with forking. Come on Citrix, you haven't bought another company for at least a few weeks now:)
The big question is - how much? Well that would be $2000 per server for the Marathon and $2500 for the Citrix per server Total: $4500. Comparatively Vmware is $5750 per two sockets. I can see people scaling up rather than out with this pricing model.
As to how this affects the market, I think it is great for the bottom end. I have at least two clients I can think of off the top of my head who would like to use virtualisation for Business Continuity purposes, but whose budgets don't extend to a SAN. From a South African perspective, (and this probably goes for most of the developing world) we are very price sensitive.
Addendum
For the sake of clarity, it should be noted that eveRun is doing a similar task the VMware's Continuous Availability. The eveRun software could - arguably- be used in lieu of HA, and this will be particularly applicable in the 3rd World. The upside of eveRun is that it is not dependant on shared storage - the same could be said to be true for VMware's Continuous Availability - the downside is that resources are required on two servers simultaneously.