One thing that may prove to be an emotional barrier to upgrading is that having your root filesystem on plain old UFS-on-disk-slices, mirrored or otherwise, is no longer an option. You must use ZFS as your root filesystem. The UFS filesystem is no longer supported as a bootable filesystem for Solaris 11.
Tip
An apparent oddity for those who are familiar with ZFS best-practices is that ZFS root pools must be made on disk slices (format entities) rather than be set to use the entire disk. Normally, this would mean that ZFS would not fully optimize write-cache use. However, for root-disk pools, ZFS makes an exception and treats them in the same way that it treats ZFS-on-whole-disk pools.