$ uname -a
Linux manwe 2.6.18-5-s390 #1 SMP Sat Dec 22 21:05:05 UTC 2007 s390 GNU/Linux
It's really dead simple to do, if you follow the instructions correctly. My host system is Debian Etch, and I'm running it on a Core 2 Duo machine with 2 gigabytes of RAM. It's relatively snappy, despite being an emulated system. Currently it's running a 31-bit kernel, but you can also run a 64-bit one as well.