The flag day for ZFS boot support was just announced which will allow for root file systems (/, /var, /usr) to be bootable from both SPARC and x86 platforms. It looks like this functionality is going to come into OpenSolaris at build 88. The install support (selecting ZFS file systems from a jumpstart profile) or from optical media looks like it’ll make its way into build 89.
A lot of people have been waiting to play with this on SPARC platforms. =) Its exciting stuff.
If you would like to find out some more information about what changes were required to the boot process to allow for ZFS root, check out the ZFS-Boot project’s website on OpenSolaris found here.