Nexenta After the Death of OpenSolaris
Solution 1:
Nexenta, Joyent, and a handful of others seem to have gotten behind Illumos
Solution 2:
Nexenta is indeed utilizing Illumos as the OS core. From what I understand, the OpenSolaris and ZFS bits they are using are truely open-sourced, and that genie can't be put back in the Sun/Oracle bottle. See this page for Nexenta's statement on this.
We are currently building out a 16TB Nexenta Enterprise box... I'll let you know how it goes. Pre-sales support experience was OK however (I had questions on zfs send/recv usage and NIS support.)
Solution 3:
I have deployed a series of boxes with Nexenta (about 250TB total deployment atm.) There was a learning curve for our Linux only shop, but all in Nexenta is a solid product and ZFS is a fantastic filesystem. I don't regret making the move at all.
Oracle has not totally killed OpenSolaris, what they have said is that instead of doing development in public, once they do a full release of Solaris 11, they will do a code dump for all the OpenSolaris community to merge in. So Nexenta will still get updates from the Oracle Devs, you will just need to wait longer.