If you're interesting in OpenIndiana, then I would follow the oi-dev mailing list. There was a recent post about the status of the project.
http://openindiana.org/pipermail/oi-...er/003496.html
But I don't think Oracle Solaris is worth spending a lot of time learning unless you have to maintain a legacy system. The licenses for Solaris (along with every other Oracle product) are outrageous to begin with, so the only people buying them are going to have a large amount of Oracle software in place already.