Suppose you had a UNIXish system which had the ability to suspend a process to disk, and then bring it back at an arbitrary later date. (There's some interesting things to think about in that alone -- how do you restore pipes, files and sockets, how do you give processes that talk to hardware the ability to have their own "restore" procedure, whether it's worth trying to identify which pages come from an executable that can be found already, how you deal with quota issues for huge processes, etc.)
This would give an easy way of implementing SunRay-like session suspending without needing to have (much) session-specific intelligence within the applications themselves.
CHPOX is an implementation of process checkpointing for Linux.