Yeah, I have been doing some research for an upcoming screencast, and this type of idea is called Operating system-level virtualization [1], and there is a fairly good table with the various OS's and their take on OS-level virtualization. E.g. Solaris Containers, FreeBSD Jail, OpenVZ, HP-UX Containers, etc.
Thanks. FYI, I just posted this to HN [1]. Seeing as you put in all this effort, you should have people reading it, outside this thread. Looks like you made the front page too!
[1] http://en.wikipedia.org/wiki/Operating_system-level_virtuali...