Support for encrypted ZFS datasets have been integrated into Solaris Next Development, build snv_148. This means that there is a good chance it will be available with the first release of Solaris 11 Express which is expected later this year.
This feature have been in the works for years with the original feature request filed in 2003. This will be a welcome addition for ZFS users with sensitive data and/or laptops.
After this only one major component is missing from ZFS, the block pointer rewrite feature. It will make it possible to encrypt/compress/deducplicate existing data in the pools as well as shrink pools and defragment them without the need to move the data out of the pool and in again.
As noted I failed to include a reference, here is bugid 4854202.
ZFS on disk encryption support
Darren in ZFS crypto video interview
ZFS crypto pushed to next year
Talks I have given
5 months ago