2 reasons for having a look at VirtualBox:
I've removed my linux slice as it's no longer used and plus I needed to extra space to move from ufs root to zfs root, but I still want to be able to load and use linux, just not waste a partition doing so.
I need to migrate from the current solaris version to the OpenSolaris code base, which uses a package manager (very much like linux).
See the notes here how the migration should occur, thanks to Bob for posting this.
Unfortunately there is a critical bugs in using VirtualBox on the latest release of the Solaris Next release i.e. it crashes the whole system!
UPDATE: This has been fixed, kudo to the VirtualBox developers, download 2.2.4 here.
So while I had been using it, to investigate VirtualBox, I can't anymore - so I decided to remove it, easy just remove the package.
However, there's always a however then next time I used liveupgrade to upgrade the system it booted ok to the console, then ran about 100 lines telling me of xVM and Network failures:
svc.startd[7]: svc:/system/xvm/ipagent:default: Method "/lib/svc/method/svc-ipagent start 60" failed with exit status 1.
The machine then went into maintenance mode 
I finally twigged that VirtualBox does some magic to the kernel and this could be causing the issue, so I reinstalled VirtualBox and then used liveupgrade.
Hey Presto a working system 