Dennis Clarke blogged about an introduction to opensolaris 2008.05, IPS, and how using ZFS (and beadm) as your root file system provides advantages with system upgrades and multiple root file systems. Take a look at his IPS-on-OpenSolaris post if you haven't yet seen IPS on opensolaris. A lot of people are really glad to see the Solaris package / patch system being revamped as its needed some attention for some time.
Speaking of Dennis and opensolaris, if you haven't ever performed a complete build, he has another OpenSolaris build walkthrough showing the entire build process of opensolaris.
Thanks Dennis! Your excitement around opensolaris rocks. And thanks for blastwave. =)