The KDE4 IPS packages that I've been working on have been rolled out at solaris.bionicmutton.org:10000 so if you are a brave soul, you could install them by adding that as a package publisher (pkg.bionicmutton.org points to the same). Something like:
pfexec pkg set-authority -O http://solaris.bionicmutton.org:10000/ kdeips
pfexec pkg install KDEgdm-integration
This will get you an /opt/foss and a /opt/kde-4.2 (the latter actually contains KDE 4.3-beta2). And you should be able to run bits and pieces from there, or even log in to KDE from the regular OpenSolaris login manager.
Getting the packages out there did have some issues. These are entirely networking related: I build them at home on one of my OSOL machines, then push them out into the IPS package server, which is running on a FreeBSD machine at the university. Since my DSL upload speed is low (about 50% faster than Jon) uploads of large files time out regularly. Pushing Qt or Boost is pretty much a no-go, as it will fall over after, say, 90MB or more. I suppose I could get on my bicycle and carry my laptop to a place where I could use the direct wired network to the server, but that would mean going outside.
Instead, I found -- relatively well-hidden, which I find typical of Sun documentation -- a wiki page that provides a nice-to-read HOWTO package which in turn points to a download page where you can get tools. The universal toolkit image is sufficient, and it contains pkg-toolkit/pkg/bin/archivepkgs.py, which will extract a package from a local repository and dump it to a tarball. In essence it defines an on-disk format for moving packages around, and you can move the tarball to another IPS repo, unpack it, and it can be served from there.
This means that I can build, publish to a repository on localhost (no network timeouts!), dump to a tarball, scp to the actual server (scp is a lot more robust in that sense than python scripts doing web-services over slow links), unpack, and there it is. It's still a 40 minute upload of Qt, but knowing that it will succeed is important.
Thanks to Kohsuke Kawaguchi for writing the original tarpkgs.py script and documenting it on his blog.