At my place of employment, 250 employee co-operative retail with three locations, I set up a 2 node DRBD/Heartbeat cluster. It is running NFS, Samba, LDAP. Clients, 42 of them, g are $275 Zotacs(Mag HD-ND01-U) running Ubuntu 10.04. I developed a disk image with everything the way we want it. It takes me 10 minutes to set up a new machine and most of that is the unboxing part. Clients authenticate via LDAP and mount NFS homes via autofs. Some apps are local such as Firefox and Thunderbird. Other business apps are accessed via A XenApp/Citrix server using the Citrix Native Linux client. And then there are the HR and Finance SAAS applications.
Now the clients could just offer a RDP connection application and the Citrix server could be a server providing virtual desktops. But why? It would add a few more layers of complexity with little benefit. The client machines are cheap, fast, easy to replace. The OS is free. The user gets the performance of silicon on the desk with the storage reliability of a server in the closet.