It varies, I have 3 identical sites, each I have specified with a max of 80 desktops, but have not came close to maxing out that number in any of the sites.
The SSD's are absolutely necessary. We've been moving users from physical machines to View due to the speed increase. One of our test View setups used 16 SATA 7200rpm drives and it was painfully slow.
The fusion-io cards will give us more performance without spending extra maintenance renewals/fees for the SSD's in our SAN.