"Hardened" and "Desktop System" are oxymorons. Using older software and careful design does not make for a "hardened" system.
I also resent Slackware Linux being grouped in with Fedora Linux. Slackware Linux is a slow-moving, carefully-built distribution built to be the most Unix-like Linux. Slackware is also the oldest Linux distribution, its team having some 10 years of experience in maintaining the Slackware system (which has legendary stability). It's design is impeccable, and I have never used a more stable system.
Fedora, on the other hand, is Red Hat's gift to the Open Source world - a beta version of Red Hat Linux. A good example of the way that Red Hat cares about the OSS community is when Fedora shipped with a buggy bootloader that made other operating systems unbootable. Would you ever find that in Slackware? Never, so please remember not to group these two distributions together.
Of course a system can be integrated when it does not even use the proper names of the applications that it contains. Sun Microsystems basically uses code that took years to develop and strips it of its identity (and thus the credit given to the hard-working group of programmers that spent so much time developing it).
JDS may be in use on Sun Opteron workstations, but I have yet to see it integrate the sort of server tools and management capabilities to migrate it away from anything but a simple desktop environment for the average user. Until then, in my mind it will simply be a small desktop distribution that does not warrant the serious consideration that can be given to SuSe and RHEL (especially now that both are being ported to more powerful architectures).
Until Sun gets serious about supporting OSS instead of just leeching without giving back anything (much less credit), I will never give JDS a consideration. I will stick with more secure, stable, and mature Linux distributions rather than Sun's latest pretty-looking dumbed-down desktop system.