things man was not meant to know.

In response to Luke's suggestion to keep pervasive snapshots of Windows using LVM -- here's a good article on direct use of the device mapper.  We've come across this stuff before (I remember my shock at the Xen LiveCD's COW system,) but this is a nice overview.  http://linuxgazette.net/114/kapil.html

Since I tend to use defaults whenever possible, I don't have free space in an LVM group to use for domUs.  Instead, I use file-backed instances.  The ability to trick the device mapper into using them like LVs is therefore invaluable.