Nexenta Core Platform 3.0 is derived from OpenSolaris Build 134, which is roughly what was supposed to be released as OpenSolaris 2010.02, then OpenSolaris 2010.03, and lastly prior to its slow death was just referred to as OpenSolaris 2010.1H. Nexenta CP 3.0 is also carrying various back-ports and other fixes onto the b134 stack.
What makes Nexenta Core Platform interesting and more than just a re-branding effort of OpenSolaris with a couple changes is that it pulls in the packages from Ubuntu 8.04 LTS. You are able to access a horde of Linux packages easily and enjoy using apt-get and other Debian package commands while benefiting from the OpenSolaris kernel and its benefits, etc. The environment is 100% Debian compatible and there's over 13,000 packages accessible from the Nexenta 3.0 repository.
Besides Nexenta Core Platform 3.0 being upgraded against OpenSolaris Build 134, this release continues to use ZFS as the default file-system, but new to version 3.0 is that ZFS de-duplication is now supported. ZFS de-duplication support was completed by Sun Microsystems last year to remove duplicate copies of data at the block-level. Other Nexenta Core Platform 3.0 changes include SMF support added for server applications, apt-clone to bring ZFS powers to apt-get, and Solaris CrossBow support.
The release announcement and brief change-log for Nexenta Core Platform 3.0 can be found at Nexenta.org. Also mentioned on their web-site is "With this release we now set direction for future releases of NCP."
While OpenSolaris may now be dead, fortunately the Nexenta project isn't getting cut off as the developers somewhat expected this to happen and earlier this month they announced Illumos, which basically is a fork of OpenSolaris. Illumos is fully open-source, is based upon OpenSolaris, and the non-OSS parts of the OpenSolaris stack have been replaced with their own open-source code. Illumos is intended to be a base for other OpenSolaris distributions like Nexenta and BeleniX. With OpenSolaris now dead in the water, it's likely future releases of Nexenta Core Platform will be based upon Illumos. It would also be nice during this transition if the Nexenta developers switched their Linux base from Ubuntu 8.04 LTS to Ubuntu 10.04 LTS.