This is awesome!
I'm a vivid FreeBSD user and as you may or may not know ZFS support has been part of that OS for quite some time. I love it. I lived the launch of ZFS on Solaris, and it was highly anticipated. Heck, us Solaris fans started being a little disappointed because several exciting features (ZFS, zones and BrandZ (virtual machines)) didn't make it into the first release of Solaris 10 but got added later on.
And ZFS has come along way since then. It's highly useful because it allows you to completely share your valuable disk space while still allowing for filesystem separation (you know: /var vs. /usr for example). And the best part: although you'll get the most out of ZFS when you set up a mirror it is not a direct requirement. You can easily use ZFS using a single hdd as well.
So with that congratulations to Ubuntu! I think this is very good news for Linux. ZFS is pretty exciting and it's a good thing that Linux users get to enjoy it also.