My Debian Linux workstation has more than 30,000 applications available. (I have most of the Debian repositories enabled.) OpenSolaris has just over 1,000. Other than the basics like OpenOffice.org, office productivity software is effectively nonexistent. The only graphics software installable via package manager is the GTHUMB image browser. To install what packages are available that way, simply go to the top Solaris menu and choose System > Administration > Package Manager. The GUI is fairly self-explanatory.
Some but not all Solaris 10 applications will work with OpenSolaris. Check the Sun site and Google for third-party packages. To install packages manually, see the link to the instructions for installing the audio driver above.
SunFreeware.com has a companion CD for Solaris with supplemental packages, but it doesn't appear to work on this build.
spec-files-extra is "a repository of RPM-like spec files for building Solaris SVr4 packages from various Open Source modules." Basically, this allows you to build your own OpenSolaris packages. If you're comfortable with source builds in Linux, you can probably make this work.
KDE has to be downloaded as a set of packages and installed manually.
MarkWilson.it has a nice list of resources for the newbie Solaris user.