I'm happy to see this. I'm only in my 20s so I haven't grown up with mainframe computing in my life, but I did get to use both an AS/400 and z/OS about 5 years ago. I've been tweeting and emailing into the dark asking IBM to just provide a free VM of one of these so I can at least play around and learn about them more. I was just getting into assembly on one when I lost access.
Having had the privilege of working with 2 different AS/400 systems (one a v4 and another a v6), I can say these guys are really bullet proof.
Rarely are the OS level issues -- almost all of our issues have been hardware (hdd's failing, not surprising though), or our vendor app messing up (too frequent to be happy about, but hey, it's written in RPG V, so can't complain too much).
The problem with learning to work with an AS/400 system is that they are ludicrously expensive to get your hands on -- So I am very glad to see something like this out there in the wild.
EDIT: Sorry, that's a link to an OS/390 VM, not AS/400. That was how I originally read your post, that you wanted a z/OS VM to play with. But, it's a useful link nonetheless ;)
