The sample application presented here is certainly a naive one, but it serves well in presenting the basic principles of RPCs. A more interesting set of applications can be found in the Network Information System (NIS) package for Linux (see the "References" section). Also, the Linux kernel sources contain an implementation of Sun's Network File System (NFS), an excellent example of the use of RPC applied to the problem of distributed file access.
In addition to distributed data access, RPC can also be used to harness the unused processing power present on most networks. The book Power Programming with RPC, listed in the "References" section, presents an image processing application that uses RPC to distribute CPU-intensive tasks over multiple processors. With RPC, you have the capability to boost the performance of your applications without spending a dime on additional hardware.