It would take a while to setup, but offensive infosec people need virtual networks to do pen testing against because they can't pen test all day every day against their own corporate network. Let the user choose a single machine or group of machines to try to compromise. Go for low cost to attract more users or go after big corporate training budgets a la sans.org

Put me in a lab of vulnerable servers and I will spend all weekend trying to get a Admin / root shell and learn way more than any books would have taught me.

BTW, computer security is sort of taking off on indeed.com http://www.indeed.com/jobtrends?q=metasploit&l=&relative=1