At VMware Forum in Oslo Fusion IO had a stand where they showed off a single HP DL380 server running 222 windows XP VMs with linked clone technology on a single Fusion IO drive. They used AutoIT to script a workload in all the VMs and you could see on four big TV screens the desktop of each windows XP desktop and the activity there.
There were Excel spreadsheets being used, Word, and other applications. By looking at the advanced performance graphs in the vSphere Client we could see that the activity generated ~32000 IOPS on average. This was across a single FusionIO card. I have to add that the cpu of that host was running constantly at 100% load. To display the remote displays on the wall they used VNC.
By using a local disk you lack functions such as VMotion, DRS, FT, etc. In a VDI environment it may not be important for everyone, but there surely are situations where you will start missing these functions. Doing administrative work during work hours will no longer be available and in a resource contention situation you will be unable to move a workload away. You may be able to solve much of this by using Storage VMotion and Storage DRS (when available), but will still require a few extra steps that may put an administrator out of the comfort zone. This can of course be solved with a virtual storage applicance or with a network clustered filesystem such as Lithium.
Some of my colleagues in Atea Denmark have been running some iometer tests of a single virtual machine and as we can see that the results are very good.
They also found that cloning of a single VM from template on RAID10 with 4 SAS disks took 330 seconds. Cloning 10 VMs on FusionIO took 202 seconds. They were also able to install a VM with Windows Server 2008R2 in 6 minutes (approx the amount of time POST takes on some newer servers).
All in all I think we can agree that this NAND Flash technology is pretty impressive and can be a solution for man IO intensive workloads such as VDI, databases, data warehouses, etc. FusionIO is currently only supported on ESX, but will soon also be supported on ESXi. While it does come up as a local disk drive, you will not be able to boot from it.