The KDE4 on OpenSolaris project carries on. The right adverb is probably "doggedly". We continue to follow KDE releases of the KDE Plasma Desktop, Applications and Frameworks. The TechBase page has been somewhat updated (although I'm not really clear on whether that kind of project belongs there or on community.kde.org). The 4.6 branch for specfiles is updated regularly and the package server is a fairly up-to-date 4.6.1 (even if it is called "4.6.0").
If you take a look at the specfiles, you will see that recently the Solaris 10 support has been revived. Ben is making great strides in getting first Qt and then the rest of the stack to compile on Solaris 10. That involves a lot more than the stack on OpenSolaris, OpenIndiana or Oracle Solaris 11 Express, because there's so much very old software that needs updating or replacing on Solaris 10.
We do bump our head on the build system, even on the newer platforms. KDE does tend to want the latest in development tools, particularly CMake. There's also a Virtuoso and a Boost update looming for us, which are also running into new and innovative compiler bugs.
We may branch out in the world and start equipping our specfiles with more compiler options -- Sun Studio is becoming problematic. Once upon a time it was a free (as in beer) compiler with some hope, somewhere, of becoming Free (as in speech), but that hope is fading fast, and the compiler with patches is now hard-to-get. We're actively considering bringing g++ on board -- that would defeat one of the original goals of the project, which was to keep KDE written C++ (as opposed to whatever dialect the current version of g++ speaks). It should be noted, though, that g++ has gotten much much better: what we really need is to turn off gcc-isms through compiler flags. Anyway, that's for future work.
For now, KDE 4.6.1 chugs along on Solaris variants -- and also still on Sun Ray thin clients, although I can recommend you don't try it on a Sun Ray 1.