My initial adventures with operating systems beyond GNU/Linux have been the UNIX types FreeBSD, OpenBSD, and Solaris8 x86.
The first was FreeBSD, which i used as firewall/router, this is now handled by OpenBSD, and Solaris for my basic interest in .jsp web development. At one time i started using FreeBSD as desktop and was impressed by it's incredible speed, but ran into issues with my USB keyboard and mouse which are connected to USB based KVM switch when i switched between desktops. This meant that i would've had to use it as a stand alone workstation with it's dedicated keyboard and mouse.
I also made attempts to use Solaris X86 for desktop use, but also ran into hardware issues. I did like the Gnome based Java Desktop even though the CDE desktop had more solaris based functionalities.
Lately since Java, Solaris, and a couple other application are freely available from Sun Microsystems, this once again peaked my interest to install Open Solaris x86 Development Edition. I initially downloaded and concatenated the Solaris Express DVDs, but it seems something went wrong along the way and wasn't able to boot the main disk.
I requested the DVDs from Sun but haven't received them yet.
BeleniX DVD 0.5.1, which is based on Open Solaris and has some of the same applications, was released so i downloaded burnt it onto a disk and proceeded to give it spin as the LiveDVD and Hadr Disk Install.