Frankly I don't see running 100 VMs as a realistic goal, being able to run Linux, Windows, Solaris and BEOS unmodified in 4-5 VMs would be far more useful.It is more than realistic. Hosting companies run more than 100 VPSs in reality. There are also other usefull scenarios. For example, I know the universities which run VPS for every faculty web site, for every department, mail server and so on. Why do you think they want to run only 5VMs on one machine? Much more!