Oracle has confirmed that they're doing something with OpenSolaris, it's not being sunk to create a diving reef or anything, so the folks who have been putting effort into KDE4 on OpenSolaris can carry on a bit. There's KDE 4.4.1 packages available (that link, which includes a specific port number, may be valid only through to mid 2010). A number of crashes has been fixed. Debugging information has been improved. There's still a little weirdness in q_atomic_decrement every now and then, but on the whole it's good to use.
It's also usable on Sun Ray 5 (which has version 4.2, I think). My OSOL machine runs SRSS (following the installation instructions on the Sun Ray wiki for OSOL 2009.6) and I can run a KDE4 session both on the local display and on the Sun Ray DTU, quite acceptably.
I took a look at the "Come out as part of KDE" guidelines, those for distro's in particular, and find that for the distributions we should (?) be writing something like this:
OpenSolaris 2010.03 comes with either GNOME 2.2.26 or Plasma Desktop 4.4 and many applications like the GIMP 2.10, Amarok 2.3.3, F-Spot, Digikam and many more.
I'm not sure why we're putting words about the available GNOME components into our distro's mouths, and the sudden (maybe I haven't been paying attention) appearance of "Plasma Desktop" is a little strange. My initial response is "that's nice, Thomas, but I wanted a Bud Lite^W^W^WKDE." Certainly because GDM's session manager is going to say "KDE" as session type, not "Plasma Desktop" for the foreseeable future.