I've been to a Sun Advertisement-Workshop two days ago. And I can just say, that they realy showed me nice things. I am going to give opensolaris a chance, soon, for sure.
Nice keywords are DTrace, Containers, and of course ZFS.
Sun offers nice documentation for their stuff, e.g. a ZFS learning center. German readers might be interessted in this blog, discussing the latest sun development, giving hints and futher links. Here is a nice video about ZFS.here is a further one.
I'm quite keen on ZFS for different reasons. According to the guy from sun we might expect encryption in autumn. Hopefully. The only flaw there might be is following one:
Data written on the ZFS is secured over checksums. Those checksums are secured over checksums, and so on. Everything is organized in trees.The root of the tree, and so the root of all checksums is the so called "uberblock". So each time data is being written, the superblock has to be updated, otherwise the change will be not visible. And this is the hot spot. To circumvent this, there are 32 copies of the uberblock, so it is not the same block written over, and over again. But the other thing is, that frequent updates (a superblock gets updated every five seconds) cause a high io-load on the disk, which may prevent powersaving methods (as suspending a disk, and so on). We will see how it will be, and what changes can be made, to improve ZFS for mobile devices.